Aggregate Structure in Heavy Crude Oil: Using a Dissipative Particle Dynamics Based Mesoscale Platform

Abstract

Heavy crude oil consists of thousands of compounds and much of them have a fairly large relative molar mass and complex structure. It is hard to learn the dynamic behavior of this fluid system at all atom models. The present study aims at constructing a mesoscale platform to explore aggregate behavior of asphaltenes in heavy crude oil. The aggregate structure in heavy crude oils was investigated by introducing rigid body fragments, which represents the significant presence of structures of fused aromatic rings in fractions such as asphaltenes and resins into dissipative particle dynamics (DPD). Another pressing task about how to determine the structure of the average model molecules and conservative force parameters was discussed in detail. With some regularity concerning the number of rings, the distribution of side chains and heteroatoms in average model molecules are revealed. Finally, we integrated the modified DPD program, model molecules, and the parameters selected for the preliminarily simulation of the heavy crude oil and emulsion system. The interlayer distance and the number of layers of the well-ordered structure in heavy crude oil are similar to some molecular dynamics works and supported by X-ray and transmission electron microscopy (TEM) experimental data. The relationship between the stability and the mass ratio among components of heavy crude oil is explored, and the result of our simulations fits the regularity Shell once published. In the emulsion system, the surfactant-like feature of asphaltenes and resins are observed. The preliminary simulation results demonstrate the validity of the rotational algorithm and parameters employed and encourage us to extend this platform to study the rheological and colloidal characteristics of heavy crude oils in the future.

Effect of acidity, hydrogenating phases and texture properties of catalysts on the evolution of asphaltenes structures during reside hydroconversion

“…12). This equal repartition explains the great number of condensed cycle units and the well known archipelago representation of asphaltenes [69]. The asphaltene representation consist in various aromatic sheets linked together through aliphatic chains.…”

A DPD study of asphaltene aggregation: The role of inhibitor and asphaltene structure in diffusion-limited aggregation

“…Realistic aggregation patterns and π − π interactions (polyaromatic ringstacking behavior) in pure heptane were obtained with the chosen asphaltene related interaction parameters, as shown earlier [8,19]. Nano-aggregates in the correct size range (∼ 2 nm and above) formed without inhibitor, provided that the asphaltene side chains contained polar groups (with or without heteroatoms in the polyaromatic core).…”

“…Nano-aggregates in the correct size range (∼ 2 nm and above) formed without inhibitor, provided that the asphaltene side chains contained polar groups (with or without heteroatoms in the polyaromatic core). The nano-aggregates displayed internal π − π stacking of the polyaromatic rings [8,7,30]. Without the polar side chain groups, the aggregates were larger and above ∼ 4 nm (with heteroatoms) or non-existent (without heteroatoms).…”

“…The asphaltene interaction parameters a ij used in the current work were calculated by Zhang and coworkers [8] 2 . Carbon and/or hydrogen in the as- heteroatoms, and only two side chains to simplify the analysis.…”

“…It is generally accepted that the asphaltene polar groups are associated mainly to nitrogen, oxygen and sulphur that can be found in the polyaromatic ring structures (as heteroatoms) and in the side chains [7,8,9]. These groups enhance self-aggregation, precipitation and adsorption [10,11].…”