Molecular Dynamics Simulation of Self-Aggregation of Asphaltenes at an Oil/Water Interface: Formation and Destruction of the Asphaltene Protective Film

Abstract

It is well known that asphaltene molecules play a significant role in stabilizing emulsions of water in crude oil or diluted bitumen solutions. Molecular dynamics simulations were employed to investigate the aggregation and orientation behaviors of asphaltene molecules in a vacuum and at various water surfaces. Two different continental model asphaltene molecules were employed in this work. It was found that the initially disordered asphaltenes quickly self-assembled into ordered nanoaggregates consisting of several molecules, in which the aromatic rings in asphaltenes were reoriented to form a face-to-face stacked structure. More importantly, statistical analysis indicates that most of the stacked polycyclic aromatic planes of asphaltene nanoaggregates tend to be perpendicular to the water surface. If the asphaltene molecules are considered as "stakes", then the asphaltene nanoaggregate can be regarded as a "fence". All the fence-like nanoaggregates were twined and knitted together, which pinned them perpendicularly on the water surface to form a steady protective film wrapping the water droplets. The mechanism of stabilization of the water/oil emulsions is thereby well understood. Demulsification processes using a chemical demulsifier were also studied. It was observed that the asphaltene protective film was destroyed by a demulsifier of ethyl cellulose molecules, leading to exposure of the water droplet. The results obtained in this work will be of significance in guiding the development of demulsification technology.

Molecular dynamic simulation of asphaltene co-aggregation with humic acid during oil spill

“…This layer hinders the direct interaction between asphaltenes and water, but serves as a surface for the accumulation of asphaltenes by parallel or T-shape stacking. The asphaltene aggregation will result in a film at the interface (Mikami et al, 2013;Liu et al, 2015). In order to confirm this deduction, we performed an extra simulation with increased concentration of asphaltene (136 g L À1 ) and LHA (100 g L À1 ) by reducing the intersection area of the interface by $42%.…”

Fractionation of Asphaltenes in Understanding Their Role in Petroleum Emulsion Stability and Fouling

“…Molecular dynamics simulation studies confirmed that asphaltene aggregation results in the formation of complex structures both in the bulk and at the oil-water interface. [43][44][45][46] The strong selfaggregation of asphaltenes facilitates the adsorption of asphaltenes at oil-water interfaces, which is crucial for the stabilization of oil-water petroleum emulsions, and also the adsorption of asphaltenes onto mineral and metallic surfaces, which leads to plugging and fouling through entire oil production chains. 38 Copyright 2010 American Chemical Society.…”

Effect of cyclohexane as hydrogen-donor in ultradispersed catalytic upgrading of heavy oil

“…Asphaltenes are the heaviest component of the feed oil composed of aliphatic side chains, polyaromatic condensed rings, metallic porphyrins (e.g., Ni and V), and heteroatoms such as sulphur, nitrogen, and oxygen [28]. They confer low API gravity, high viscosity to the feed oil and subsequently their precipitation during upgrading reactions contribute majorly to coke formation.…”