Effect of resin/asphaltene ratio on the rheological behavior of asphaltene solutions in a de-asphalted oil and p-xylene: A theoretical–experimental approach

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

“…Molecular structures representing the experimental systems in molecular dynamics simulations: (a) average molecular structure of asphaltene and (b–e) molecular structures of the solvent evaluated: benzene, o -xylene, m -xylene, and p -xylene. [The asphaltene molecular structure is reproduced with permission from ref . Copyright 2020.…”

“…The OPLS-aa potential (optimized potentials for liquid simulations) , was used to describe the experimentally evaluated asphaltene solutions (Figure ). This potential has been widely used to describe organic substances such as n -C 7 asphaltene molecules and the solvents evaluated in this study. ,,, Intermolecular interactions, i.e. van der Waals and electrostatics, were described using the 12–6 Lennard–Jones and Coulombic models, respectively.…”

“…n- C7 asphaltenes are amphiphilic poly aromatics hydrocarbons (PAHs) with a strong tendency to form aggregates due to their self-associative behavior. − This crude oil fraction is by definition insoluble in alkyl short-chain solvents (i.e., n -pentane or n -heptane) and soluble in aromatic solvents (i.e., benzene, toluene, and xylene), which are the most common solvents used for isolating asphaltenes in the oil and gas industry. , This self-associative behavior of asphaltenes has a substantial impact on the production , and transportation , of crude oil because it reduces the area available for crude oil flow (in the porous medium or pipes) and increases crude oil viscosity due to the formation of viscoelastic networks . For this reason, numerous studies have focused on proposing alternatives to avoid asphaltene aggregation to mitigate the damage caused by asphaltene precipitation and deposition. ,, Model solutions have been widely used for this purpose.…”

“…A model solution is frequently used as a simplified representation of crude oil, composed of asphaltene in aromatic and/or aliphatic solvents. − Typically, toluene , and n -heptane ,, are used separately or in a mixture referred to as a heptol. Several authors have used model solutions to characterize the physical aggregation and rheological behavior of heavy crude oils. ,,− Asphaltenes are obtained by a sequential washing procedure of a given crude oil with aliphatic solvents ( n -pentane or n -heptane), the details of which have been extensively detailed in the literature. ,, …”

“…Theoretical studies based on computational molecular simulations have made it possible to elucidate phenomenological aspects of asphaltene aggregation and their impact on viscosity. ,,,, Using model solutions to develop an atomistic description of the experimentally evaluated systems has permitted researchers to establish ideas concerning asphaltene aggregation mechanisms, ,,− viscosity determinations, ,,, and other phenomena. One of the most important, and perhaps most controversial activities, is representing the entire complexity of the asphaltene fraction of crude oil in an average molecular structure or a group of molecular structures. ,,− Therefore, several studies focused on proposing adequate molecular structures which allow a reliable representation of the physical behavior of a specific asphaltene type. ,,, Numerous investigations have focused on determining the mechanisms of asphaltene aggregation in n -heptane and toluene using molecular dynamics. ,,, The results indicate that asphaltene aggregation is promoted in both solvents. ,− Furthermore, authors have identified that the aggregation of asphaltenes in organic solvents, such as n -heptane or toluene, occurs via van der Waals type energies and the π–π interactions between the aromatic nuclei of asphaltene molecular structures. ,,, In contrast, the behavior of asphaltene molecules dissolved in polar solvents, such as water, are determined to a greater extent by electrostatic interactions and the formation of hydrogen bonds than van der Waals interactions. − …”