Asphaltene Aggregation under Vacuum at Different Temperatures by Molecular Dynamics

Abstract

Asphaltene aggregation under vacuum at different temperatures was obtained using classical molecular dynamics (MD) simulations under nonperiodic boundary conditions in a monodisperse system of 96 hypothetical asphaltene molecules. Identical asphaltenes were originally set as an array, where the separation between each other was ∼40 Å. Simulations under the canonical ensemble at NVT conditions, using the Verlet numerical method to solve the motion equations, were conducted. Aggregated systems formed by several asphaltene monomers after 100 ps of classical MD simulations were found. The structure of the solution was analyzed using the radial distribution function. Simulations at four different temperatures (273, 312, 342, and 368 K) were accomplished. Another similar MD simulation at a temperature of 310 K for 300 ps was performed, to validate the stability in the previous systems. After this run, good structures for explaining asphaltene interactions were also observed; these structures were never before proposed. The following effects can be observed from the results: (i) aggregates that have different structures indicate different types of interactions; (ii) decreasing aggregation number values with increasing temperature is consistent with experimental reality; (iii) the average molecular weights obtained for different temperatures agree with the expected range of experimental values; and (iv) the minimum of the potential energy well, in the range of 3.5-4.0 Å, is consistent with the Yen model.

The influence of asphaltene-resin molecular interactions on the colloidal stability of crude oil

“…In addition, our result is comparable with those from Molecular Dynamics (MD) simulations that reported an interlayer distance of 3.5-4 Å [73,81].…”

“…The energy values reported here seem to be remarkably lower than À55 kcal/mol, the value reported by Pacheco-Sánchez et al [73] for one asphaltene dimer in a vacuum using COMPASS Force Field [74,75], derived using classical Molecular Mechanics (MM) for a parallel arrangement with binding distance of 4 and 5 Å. In another study [76] based on MM and semiempirical calculations, the interaction energy was reported to be À45 kcal/mol for two asphaltene dimers, each containing a hydroxyl group.…”

“…The presence of heteroatoms in asphaltene sheets and also in peripheral chains causes a wider intermolecular orientation distribution even for the simulation of a dimer, the simplest form of asphaltene aggregate. There are four most commonly proposed arrangements for an asphaltene dimer: parallel or face-to-face (p-p interaction); parallel-displaced or offset (r-r interactions); T-shape or face-to-edge (p-r interactions); and Tshape or edge-to-edge (r-r interactions) [71][72][73].…”

Quantitative Molecular Representation of Asphaltenes and Molecular Dynamics Simulation of Their Aggregation

“…In recent years there has been an increasing effort to understand asphaltene aggregation on a molecular level using molecular simulation 15,16,17,18,19,20 . The Quantitative Molecular Representation (QMR) method is a vital tool for generating molecular structures for asphaltene simulation.…”

Non-Newtonian behavior and molecular structure of Cooee bitumen under shear flow: A non-equilibrium molecular dynamics study

“…Molecular dynamics (MD) is a good tool to study the molecular structure of bitumen and of the asphaltene nanoaggregates [12][13][14][15]. MD simulations can also quantify the mechanical properties of the material.…”