Computational Simulation of Asphaltenes: The Effect of Concentration on
Dissociation of the Aggregate in Solvent Mixtures.
Alexandre N. M. Carauta1,* , Peter R. Seidl2, Júlio C. G. Corrêia3.
1
Departamento de Química Inorgânica. Instituto de Química. Universidade Federal
Fluminense – UFF. Niterói – RJ. Brazil
2
Departamento de Processos Orgânicos, Escola de Química, Universidade Federal do Rio de
Janeiro - UFRJ. Rio de Janeiro – RJ. Brazil.
3
Coordenação de Apoio a Pequena e Média Empresa do Centro de Tecnologia Mineral –
CETEM. Rio de Janeiro – RJ.
*
Speaker e-mail: [email protected]
Solvent extraction is widely used in separations of lighter hydrocarbons from heavy residues.
In industrial practice, however, solvents are usually mixtures of isomers or of similar classes
of compounds. Mixtures of solvents have also been employed to separate asphaltenes and
other constituents of heavy oils into representative fractions. Since molecular dynamics
simulations could be successfully employed to predict the tendency of asphaltene dimers to
dissociate in the presence of common solvents, we used a similar approach to investigate their
behavior in mixtures. of these solvents. For the sake of comparison, we calculated energyminimum conformations for monomer, dimer and amorphous structures of “clean”
asphaltenes that were used in our previous studies in the presence of varying proportions of nbutane and isobutane. The Hildebrand solubility parameter for the average model structure
was calculated to validate the model and the results obtained for the dimer are in agreement
with experimental ones. The effect of temperature on the asphaltene aggregates, at 323 and
400 K, could also be monitored during the simulation time, showing that distances between
the monomers are not hardly affected by temperature. Thus increases in distances observed
during simulation in the presence of solvents and their mixtures must be owing to interactions
among asphaltenes and-solvents. The degree of dissociation depends on the proportion of nto isobutane in the mixture and, except at high dilution, dissociation takes place to a lesser
extent in mixtures than in isolated solvents.