Investigating the Compatibility of Various Components in Marine Low-Sulfur Fuel Oil by Molecular Dynamics Simulations

Abstract

Asphaltene aggregation and precipitation are one of the major issues for marine low-sulfur fuel oil used on board. Many research studies have been carried out to investigate the aggregation behavior of asphaltene under different conditions, but the mechanism of asphaltene aggregation in low-sulfur fuel oil at the molecular level is still unclear. In this work, molecular dynamics (MD) simulations were performed to calculate the solubility parameters, intermolecular interaction energies, and radial distribution function (RDF) curves of each component in marine low-sulfur fuel oil to examine their mutual compatibility. Simulation results indicate that the solubility parameter of resin gains the highest value and it is close to asphaltene. The solubility parameters of aromatic, hexadecane, and saturate decrease successively. The interaction energy between resin and asphaltene molecules is higher than that between the same kind of molecules, which means that resin can inhibit the aggregation of asphaltene molecules. Typically, a light distillate component (hexadecane) is added to heavy fuel oil to yield low-sulfur oil, and our calculations reveal that this has a negative effect on asphaltene aggregation. Specifically, asphaltene is more likely to self-aggregate, as shown by the increase in peak height in the radial distribution function of the asphaltene-asphaltene pair. The findings of this study will provide theoretical support for the production of marine low-sulfur fuel.

Evaluation of Asphaltene Hildebrand and Hansen Solubility Parameters Using Digital Oil Models with Molecular Dynamics Simulation

“…CHNS elemental analysis determined carbon, hydrogen, nitrogen, and sulfur content ratios. In addition, 1 H NMR and 13 C NMR analyses were conducted to determine the molecular structure, that is, the structural types of hydrogen and carbon atoms. These analytical results were applied to the QMR method 74 to generate molecular models for asphaltene.…”

“…9,10 For instance, the solubility testing of both asphaltenes and maltenes was performed, explaining how asphaltenes are present in heavy crude oil (such as bitumen) in terms of mutual solubility and internal stability. 11 Several thermodynamic models have been developed to predict asphaltene precipitation based on solubility, 1,[8][9][10]12 which can also be used to evaluate the compatibility of blending, 11,13 and so on. These studies concerning asphaltene solubility are based on the fundamental assumption that asphaltenes are considered solid substances dissolved within a solvent composed of the other components in crude oil.…”

“…Molecular dynamics (MD) simulation is an effective approach for predicting macroscopic properties resulting from specific microscopic molecular interactions and structures. ,,,,− In line with HSP principles, Khafal and Mansoori conducted MD simulations to reveal the contribution of van der Waals (vdW), electrostatic, and hydrogen bonding to the aggregation of asphaltene molecules by constructing three different structures of asphaltene molecules and a simple crude oil model consisting of heptane and o -xylene. Using different asphaltene molecular models, including models for two subfractions of asphaltenes, A1 with a rigid core that tends to aggregate easily, A2 with higher flexibility in structure and better solubility in toluene, a highly aromatic island model, and archipelago-type model, the aggregation behavior was studied. − The asphaltene aggregates were observed in various solvents even at low concentrations. , Further investigations revealed that the simulated system exhibited size distribution profiles similar to the gel permeation chromatography (GPC) experimental analyses of asphaltene samples in tetrahydrofuran (THF). , Interestingly, Villegas et al showed that the dipole moment of asphaltene aggregate tends to be zero when the number of molecules in the aggregate increases.…”

“…However, the determination of asphaltene HSPs through MD simulation has remained challenging. Recent research has attempted to separate the solubility parameter of asphaltenes into two terms accounting for dispersion and Coulomb contributions, without further distinguishing the δ P (polar) and δ H (hydrogen bonding) components from the overall electrostatic interaction. ,, To the best of our knowledge, no successful attempt has been made thus far to determine the HSPs of asphaltenes using MD simulation.…”

“…Compared to the challenging tasks of determining the specific structure of each molecule, asphaltene solubility has been regarded as a convenient tool for explaining and resolving numerous problems, and it stands as one of the key properties for characterizing asphaltene deposition. , For instance, the solubility testing of both asphaltenes and maltenes was performed, explaining how asphaltenes are present in heavy crude oil (such as bitumen) in terms of mutual solubility and internal stability . Several thermodynamic models have been developed to predict asphaltene precipitation based on solubility, ,− , which can also be used to evaluate the compatibility of blending, , and so on. These studies concerning asphaltene solubility are based on the fundamental assumption that asphaltenes are considered solid substances dissolved within a solvent composed of the other components in crude oil. , In describing the dissolution process, the principle is “like dissolves like”, and the concept of “solubility parameter” has been introduced to quantify the similarity between substances using simple numerical values. , In other words, substances with similar solubility parameters are mutually soluble.…”