Simulation of asphaltene aggregation through molecular dynamics: insights and limitations
File(s)
Published version
Author(s)
Headen, T
Boek, E
Jackson, G
Totton, T
Muller, EA
Type
Journal Article
Abstract
We report
classical
atomistic molecular dynamics simulations of four structurally diverse model
asphaltenes, a model resin
,
and their
respective
mixtures in toluene or heptane at ambient
conditions.
Relatively large
systems (~50,000 atoms) and long timescales
(> 80 ns)
are explored.
Where
ever possible
,
comparisons are made
to available experimental observations asserting the
validity of the models.
W
hen
the
asphaltenes are dissolved in toluene,
a continuous distribut
ion
of cluster sizes
is observed
with average aggregation number ranging between 3.6
and
5.6
,
monomers and dimers
being the
predominant
species
. As expected for mixtures
in heptane
the
asphaltene molecules
tend to aggregate to form a segregated phase. There is no evidence of a
distinct formation of nanoaggregates, the distributions of clusters
is found to be
continuous
in
character.
The
analysis
of the shape of the clusters of asphaltenes
suggests that
they
are generally
spherical in
character, with the archipelago models favouring longer prolate
structures
and the
continental
model
tending towards
oblate
structures
. The aggregates are
seen to be
diffuse in
nature, containing at least 50% solvent
on average
, being denser in heptane than in toluene.
M
ixtures of asphaltenes with different
architecture
are found to have
cluster properties that are
intermediate between those of the individual components. The presence of resins in the mixture
does not
appear
to
a
lter the
shape of the
asphaltene aggregate
s
,
their
size or density when toluene
is the solvent;
on the other
hand the
resins
lead to an
increase
in
the density of the resulting
aggregates
in heptane
.
Quantification of these observations is made
from the
hi
stograms of
cluster distributions,
the
p
otential of mean force calculations
,
and
an
analysis of
the
shape
factors
. We
illustrate how
the time scales for
complete aggregation
of molecules in heptane
are
larger than the longest of
the
simulations reported
in the open literature and as an example report
a long simulation
(0.5 μs)
which fails to reach an equilibrium state
, suggesting that
acceleration
techniques
,
for example
, using
coarse grained models
,
are needed
to
appropriately
explore these
phenomena.
classical
atomistic molecular dynamics simulations of four structurally diverse model
asphaltenes, a model resin
,
and their
respective
mixtures in toluene or heptane at ambient
conditions.
Relatively large
systems (~50,000 atoms) and long timescales
(> 80 ns)
are explored.
Where
ever possible
,
comparisons are made
to available experimental observations asserting the
validity of the models.
W
hen
the
asphaltenes are dissolved in toluene,
a continuous distribut
ion
of cluster sizes
is observed
with average aggregation number ranging between 3.6
and
5.6
,
monomers and dimers
being the
predominant
species
. As expected for mixtures
in heptane
the
asphaltene molecules
tend to aggregate to form a segregated phase. There is no evidence of a
distinct formation of nanoaggregates, the distributions of clusters
is found to be
continuous
in
character.
The
analysis
of the shape of the clusters of asphaltenes
suggests that
they
are generally
spherical in
character, with the archipelago models favouring longer prolate
structures
and the
continental
model
tending towards
oblate
structures
. The aggregates are
seen to be
diffuse in
nature, containing at least 50% solvent
on average
, being denser in heptane than in toluene.
M
ixtures of asphaltenes with different
architecture
are found to have
cluster properties that are
intermediate between those of the individual components. The presence of resins in the mixture
does not
appear
to
a
lter the
shape of the
asphaltene aggregate
s
,
their
size or density when toluene
is the solvent;
on the other
hand the
resins
lead to an
increase
in
the density of the resulting
aggregates
in heptane
.
Quantification of these observations is made
from the
hi
stograms of
cluster distributions,
the
p
otential of mean force calculations
,
and
an
analysis of
the
shape
factors
. We
illustrate how
the time scales for
complete aggregation
of molecules in heptane
are
larger than the longest of
the
simulations reported
in the open literature and as an example report
a long simulation
(0.5 μs)
which fails to reach an equilibrium state
, suggesting that
acceleration
techniques
,
for example
, using
coarse grained models
,
are needed
to
appropriately
explore these
phenomena.
Date Issued
2017-01-03
Date Acceptance
2017-01-03
Citation
Energy & Fuels, 2017, 31 (2), pp.1108-1125
ISSN
1520-5029
Publisher
American Chemical Society
Start Page
1108
End Page
1125
Journal / Book Title
Energy & Fuels
Volume
31
Issue
2
Copyright Statement
© 2017 American Chemical Society. This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes (http://pubs.acs.org/page/policy/authorchoice_termsofuse.html)
Sponsor
Engineering & Physical Science Research Council (EPSRC)
Engineering & Physical Science Research Council (EPSRC)
BP International Limited
Grant Number
EP/E016340/1
EP/J014958/1
75195/ICAM15 (All) WS2
Subjects
Science & Technology
Technology
Energy & Fuels
Engineering, Chemical
Engineering
ATOMIC-FORCE MICROSCOPY
ANALYZING PETROLEUM ASPHALTENES
SIZE-EXCLUSION CHROMATOGRAPHY
ANGLE NEUTRON-SCATTERING
CRUDE OILS
MODEL
SYSTEMS
NANOAGGREGATION
REPRESENTATION
MECHANICS
Energy
03 Chemical Sciences
09 Engineering
Publication Status
Published