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Molecular Dynamics Simulation of Self-Aggregation of Asphaltenes at an Oil/Water Interface: Formation and Destruction of the Asphaltene Protective Film
journal contribution
posted on 2015-12-17, 07:21 authored by Juan Liu, Yapu Zhao, Sili RenIt 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.