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

Abstract

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.

Structural-Compositional Effect of Polycyclic Aromatic Hydrocarbons on Thermal-Oxidative Decomposition at High-Pressure: A Molecular Dynamics and Machine Learning Approach

“…There is a substantial lack of studies in the literature regarding both approaches, especially compared to experimental studies, which, in some cases, cannot be generalized beyond the samples investigated . Molecular dynamics (MD) simulations are a deterministic tool that can be used to derive physical insights regarding the relationship between macroscopic behaviors and structural and compositional characteristics. , Chen et al developed an MD model using reactive force fields (REAX-FF) to describe char oxidation processes in air, CO 2 , and O 2 –CO 2 atmospheres. The authors found that the O radical and CO 2 could adsorb and destroy the edge of representative PAH molecules in the char model during char oxidation and gasification.…”

Reconstruction of a Synthetic Crude Oil Using Petroleomics and Molecular Dynamics Simulations: A Multistructural Approach to Understanding Asphaltene Aggregation Behavior

“…This is related to the synergetic interaction between the asphaltene molecules and the solvent, which was reported in the literature evaluating the aggregation and rheological behavior of asphaltenes dissolved in benzene and xylene isomers. 62 These results indicate that a multistructural description of asphaltenes not only allows for the data from the experimentally determined elemental analysis to be more adequately represented but also could be a suitable representation of the aggregation behavior. This is based on the fact that the aggregation states of the uniand multistructural approximation evaluated were different and considering that the multistructural representation describes the species determined experimentally by FTC-IR MS.…”

“…Despite their aggregation sizes being similar, their internal structures are substantially different, since maltene solvent contents resin and aromatics species that has a strong effect on the aggregation and rheological behavior of asphaltenes systems. This is related to the synergetic interaction between the asphaltene molecules and the solvent, which was reported in the literature evaluating the aggregation and rheological behavior of asphaltenes dissolved in benzene and xylene isomers . These results indicate that a multistructural description of asphaltenes not only allows for the data from the experimentally determined elemental analysis to be more adequately represented but also could be a suitable representation of the aggregation behavior.…”

PetroPhase2021 Virtual Special Issue

“…9 In another paper, they characterized the rheological behavior of asphaltenes dissolved in benzene and xylene isomers to understand the solvent effect. 10 Hristova and Stoyanov reported that asphaltene precipitation starts and increases gradually rather than abruptly, and a new hypothesis was proposed to explain this difference with a conventional understanding of critical dilution. 11 Rogel et al investigated the fouling propensity of crude oil blends and found that the main driving force behind fouling seems to be related to the compatibility of the components.…”

“…In the first paper, they used petroleomics and molecular dynamics simulations to reconstruct a synthetic crude oil to understand the asphaltene aggregation behavior . In another paper, they characterized the rheological behavior of asphaltenes dissolved in benzene and xylene isomers to understand the solvent effect . Hristova and Stoyanov reported that asphaltene precipitation starts and increases gradually rather than abruptly, and a new hypothesis was proposed to explain this difference with a conventional understanding of critical dilution .…”