Molecular Dynamics Study of the Aggregation Behavior of Polycyclic Aromatic Hydrocarbon Molecules in n-Heptane–Toluene Mixtures: Assessing the Heteroatom Content Effect

Abstract

This study is focused on evaluating the aggregation behavior of four asphaltene molecules (PA3-type) dissolved in three different solvents. Hence, solution models composed of asphaltenes dissolved in toluene, n-heptane, and mixtures of n-heptane and toluene (known as heptol), were evaluated with molecular dynamics (MD) simulations. For MD calculations, four PA3-type structures were chosen to evaluate the effect of the location of one heteroatom in the polyaromatic core on the aggregation behavior. The first structure consists of only a CH structure, the second has sulfur, the third has nitrogen, and the last one contains oxygen. The heteroatom was replaced in the same location in one of the five-membered rings in the center of the molecule to test the different chemical effects induced by these heteroatoms. Molecules with the heteroatoms showed a higher aggregation tendency in n-heptane than in heptol-50 and toluene, with an average size of 12.8, 6.2, and 2.4 molecules per aggregate, respectively, whereas the PA3 molecule with no heteroatom forms less and smaller aggregates. The inclusion of only one heteroatom increases the polarity and the planarity of the molecule, increasing the attractive interaction energies (140−160% in n-heptane) and the overall aggregation tendency. The molecule with the sulfur heteroatom forms bigger and more stable aggregates than molecules with oxygen and nitrogen. In conclusion, the inclusion of heteroatoms in the PA3 structure increases the polarity and planarity of the molecule, improving the aggregation tendency in all solvents, notoriously in n-heptane.

Computing contact angles for oil–water–rock systems via thermodynamic integration

“…[46][47][48] For this study, we concentrate on the aliphatic portion and use n-heptane as the model aliphatic fluid since it has been used as a representative for the light alkanes in a number of molecular dynamics studies. [49][50][51][52][53][54][55][56] The interactions of n-heptane are described by the TRaPPE force field. 57 Liquid water was modeled by the extended simple point charge model (SPC/E) force field.…”

Viscosities and Densities of Binary and Ternary Mixtures of Aliphatic and Polyaromatic Hydrocarbons: Pyrene +1-Methylnaphthalene + Dodecane at T = (293.15 to 343.15) K. Experiment and Modeling

“…While there is still a limited scope of experimental studies on the properties of aromatic hydrocarbons and their mixtures, , recent publications have explored the combination of experimental and theoretical approaches, such as molecular dynamics (MD), to investigate thermophysical properties such as viscosity and density. For instance, studies have been conducted on mixtures of cyclohexanes and alkyl cyclohexanes with n -paraffins − and alkylbenzenes with linear alkanes. , …”

“…Group contribution (GC) methods require a binary interaction parameter matrix . More theoretical methods include quantitative structure–property relationships, equations of state (EoS), and molecular dynamics. ,, …”

“…17 More theoretical methods include quantitative structure−property relationships, equations of state (EoS), 15 and molecular dynamics. 10,11,13 Recently, methods based on EoS have received high attention. Guo et al (2001) 18 used the Peng−Robinson equation's formulation and transformed the variables T−V−P to P−η−T.…”

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

“…In the last 10 years, molecular dynamics (MD) simulations have become a commonly used theoretical tool to obtain physical insights in the context of the oil and gas industry. , Topics of interest include understanding the role of asphaltenes in three main phenomena: aggregation, ,− adsorption, − and interfacial tension. ,− Aggregation is related to understanding the self-interactions of asphaltenes in solvents; typical solvents include n -heptane, toluene, or a mixture (Heptol). ,− Adsorption is related to the ability of the asphaltenes to adsorb onto a mineral or metal surface, as well as its ability to alter the wettability state of that surface. ,, Finally, interfacial tension is related to the role of the asphaltenes with regards to the water–oil or brine–oil interface. , In each of the cases described above, the confidence of the results obtained by in silico evaluations is strongly dependent on the reliability of the representation of the system, especially with regards to asphaltenes. ,,, Hence, some researchers have focused on proposing suitable asphaltene molecular structures that represent their physical behavior, without reaching a single representation of this fraction. − In many cases, a single average structure is used to describe the full complexity of asphaltenes. ,,− One of the first studies that used MD was published by Rogel, in which the aggregation behavior of asphaltenes was evaluated by considering two average molecular structures. Although the molecular weights and distribution of the π-electrons were not assigned properly according to the sextet Clar’s rule, the results were a valuable contribution to understanding the aggregation mechanism of asphaltene molecules.…”