This study characterized the rheological
behavior of asphaltenes
dissolved in aromatic solvents of different chemical nature to understand
the solvent effect. For this purpose, n-C7 asphaltenes were obtained from extra-heavy crude oil and dissolved
at three concentrations (1, 8, and 15 wt %) in solvents with different
molecular structures: benzene and three xylene isomers. The experimental
results revealed appreciable differences in the viscosity of the asphaltene
solutions in each solvent which were more marked at higher concentrations
(>1 wt %) of n-C7 asphaltenes. Molecular
dynamics simulations were conducted to characterize some physical
aspects that result in rheological differences. The average aggregate
sizes, mean square displacement, asphaltene–asphaltene and
asphaltene–solvent interaction energies, and solubility parameters
were calculated. The smallest aggregation size was obtained for solutions
in o-xylene, followed by m-xylene
and p-xylene. Although benzene promoted greater asphaltene
aggregation (similar to that obtained with p-xylene),
it did not provide the highest viscosity. This result is due to the
synergic interactions between the asphaltene aggregate and the solvent,
which modified the fluid’s internal friction, evidenced macroscopically
as a higher viscosity. Therefore, asphaltene aggregates demonstrated
freer movement in benzene than in p-xylene. The main
difference between the three xylene isomers corresponds to the dipole
moment and solubility parameter due to the location of the −CH3 substituent. This study improves our understanding of the
relationship between the aggregation and rheological behavior of crude
oils, characterizing the physical behavior to propose alternatives
that reduce asphaltene aggregation and its viscosity.