Physical Insights about Viscosity Differences of Asphaltene Dissolved in Benzene and Xylene Isomers: Theoretical-Experimental Approaches

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-C-7 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-C-7 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. Therefor; 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.

Automated summary

This study investigated the rheological behavior of asphaltenes dissolved in aromatic solvents of different chemical nature through experiments and molecular dynamics simulations. Significant differences in viscosity of asphaltene solutions in different solvents were found, attributed to synergic interactions between asphaltene aggregates and solvents. The smallest aggregation size was observed in o-xylene solutions, indicating the impact of solvent type on asphaltene behavior.