Mesoscopic probes in asphaltenes nanoaggregate structure: from perpendicular to paralleled orientation at the water-in-oil emulsions interface

Chen, Jin‐hui; Chen, Jinliang; Zhong, Chuheng; Chen, Shouyu; Chen, Bowen; Fang, Shenwen; Xiang, Wei

doi:10.1039/c7ra06717h

Cited by 20 publications

(21 citation statements)

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“…To date, the main characteristics of the original Yen model are still the basis of asphaltene science: clusters of aromatic cores in which π-stacking is the major, if not the only , intermolecular force responsible for asphaltene aggregation. − It is believed that the dominant molecular motif consists of a single polycyclic aromatic hydrocarbon (HC) of ∼7 fused rings, with an average molecular weight of ∼750 g/mol, known as island . − The aromatic cores are polarizable and exhibit induced dipole–dipole interactions that become stronger as a function of increasing aromatic core size . The influence of heteroatoms was largely limited to their effect within the aromatic cores, such as in pyridine and furan groups, where they promote charge separation, leading to dipole–dipole interactions.…”

Section: Introductionmentioning

confidence: 99%

Advances in Asphaltene Petroleomics. Part 4. Compositional Trends of Solubility Subfractions Reveal that Polyfunctional Oxygen-Containing Compounds Drive Asphaltene Chemistry

et al. 2020

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Asphaltenes have traditionally been conceived as highly aromatic, alkyl-deficient compounds enriched in pericondensed aromatic “island” motifs. This structural definition evolved into the general notion that aromatic core-dominated interactions (π-stacking) drive asphaltene aggregation, and heteroatom-based intermolecular forces have no significant effect on the overall solubility and aggregation behavior. However, the exclusion of heteroatoms in asphaltene chemistry is inconsistent with the Boduszynski continuum and known asphaltene properties, such as increased heteroatom content relative to maltenes, interfacial activity, and strong adsorption to polar stationary phases. Thus, to determine whether or not heteroatoms are involved in solubility, we have separated asphaltene fractions enriched in single-core (island) or multicore motifs (archipelago) according to their partitioning in n-heptane by two fractionation methods. In the first separation procedure, the acetone fraction from Wyoming deposit n-heptane asphaltenes (island-enriched) was adsorbed on polytetrafluoroethylene powder and Soxhlet extracted with n-heptane. Subfractions were collected after one day, one week, one month, and three months of extraction, and the residue, n-heptane insoluble material, was recovered with a mixture of toluene and dichloromethane. In the second method, the acetone fraction from Athabasca bitumen n-heptane asphaltenes (archipelago-enriched) was fractionated by differential precipitation in mixtures of n-heptane and toluene. The molecular composition of the asphaltene subfractions was accessed by positive-ion atmospheric pressure photoionization coupled to 9.4 T Fourier transform ion cyclotron resonance mass spectrometry and structures were determined by infrared multiphoton dissociation. The compositional trends for heteroatom content, double bond equivalents, and alkyl substitution suggest that the Boduszynski continuum can be extended to asphaltenes. In particular, the compositional range of polyoxygenated asphaltene compounds shifts toward lower aromaticity, whereas oxygen-depleted species are more aromatic. Moreover, the results demonstrate that polyoxygenated species (e.g., O3 and S2O3 classes) are pivotal in asphaltene solubility, as they concentrate in the most polarizable and insoluble asphaltene subfractions. Therefore, the results support the existence of atypical asphaltene species with remarkably low aromaticity that reside in the most insoluble asphaltene subfractions because of their high heteroatom content. Such asphaltene compounds preferentially ionize as protonated molecules rather than radical cations and overlap the compositional range of interfacially active species, consistent with their tendency to participate in hydrogen bonding. Collectively, the results highlight the need for an asphaltene molecular model based on the existence of polyfunctional species capable of interacting with neighboring asphaltene molecules through several intermolecular forces, including London dispersion forces between ali...

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Section: Introductionmentioning

confidence: 99%

Advances in Asphaltene Petroleomics. Part 4. Compositional Trends of Solubility Subfractions Reveal that Polyfunctional Oxygen-Containing Compounds Drive Asphaltene Chemistry

et al. 2020

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“…To model the aromatic cores in the asphaltene and resin models, the authors proposed a rigid sheet of particles representing fused aromatic rings, arranged to preserve the aromatic-core topology. Other work that involve molecular simulations of asphaltenes described at a coarse-grained level are presented in refs , − .…”

Section: Introductionmentioning

confidence: 99%

Aggregation Behavior of Model Asphaltenes Revealed from Large-Scale Coarse-Grained Molecular Simulations

et al. 2019

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Fully atomistic simulations of models of asphaltenes in simple solvents have allowed the study of trends in aggregation phenomena and the understanding of the role that molecular structure plays therein. However, the detail included at this scale of molecular modeling is at odds with the required spatial and temporal resolution needed to fully understand the asphaltene aggregation. The computational cost required to explore the relevant scales can be reduced by employing coarse-grained (CG) models, which consist of lumping a few atoms into a single segment that is characterised by effective interactions. In this work CG force fields developed via the SAFT-γ [Müller, E.A., Jackson, G. (2014) Annu. Rev. Chem. Biomolec. Eng., 5, 405-427] equation of state (EoS) provide a reliable pathway to link the molecular description with macroscopic thermophysical data. A recent modification of the SAFT-VR EoS [Müller, E.A. and Mejía, A. (2017) Langmuir, 33, 11518-11529], that allows parametrizing homonuclear rings, is selected as the starting point to propose CG models for polycyclic aromatic hydrocarbons (PAHs). The new aromatic-core parameters, along with others published for simpler organic molecules, are adopted for the construction of asphaltene models by combining different chemical moieties in a group-contribution fashion. We apply the procedure to two previously reported asphaltene models and perform Molecular Dynamics simulations to validate the coarse-grained representation against benchmark systems of 27 asphaltenes in pure solvent (toluene or heptane) described in a fully atomistic fashion. An excellent match between both levels of description is observed for cluster size, radii of gyration, and relative-shape-anisotropy-factor distributions. We exploit the advantages of the CG representation by simulating systems containing up to 2000 asphaltene molecules in explicit solvent investigating the effect of asphaltene concentration, solvent composition, and temperature on aggregation. Upon employing large systems facilitated by the CG models, we observe stable continuous distributions of molecular aggregates at conditions away from the two-phase precipitation point. As a further example application, a widely accepted interpretation of cluster-size distributions in asphaltenic systems is challenged by performing system-size tests, reversibility proofs and time-dependence analysis. The coarse-graining procedure proposed is seen to be general and predictive, hence, can be applied to other asphaltenic molecular structures.

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“…At higher concentrations, these aggregates form clusters, which have smaller binding energies than the ones occurring within the nanoaggregates. Molecular dynamics simulations (MD) and dissipative particle dynamics (DPD) are consistent with the presence of nanoaggregates, in bulk, − and at liquid/liquid interfaces. , …”

Section: Introductionmentioning

confidence: 74%

“…Molecular dynamics simulations (MD) and dissipative particle dynamics (DPD) are consistent with the presence of nanoaggregates, in bulk, 13−15 and at liquid/liquid interfaces. 16,17 Asphaltenes are typically one of the more polar fractions in crude oils and their chemical features, and possibly their colloidal nature (when present as nanoaggregates) make them prone to strongly adsorb at the oil/water interface due to the high capillary energy of colloidal nanoaggregates. 18 Asphaltene adsorption does, however, not only lead to a change in interfacial tension, but the formation of elastic skins around droplets has been reported.…”

Section: ■ Introductionmentioning

confidence: 99%

Assessing the Interfacial Activity of Insoluble Asphaltene Layers: Interfacial Rheology versus Interfacial Tension

Alicke

Simon²,

Sjöblom³

et al. 2020

Langmuir

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Asphaltenes have been suggested to play an important role in the remarkable stability of some water-in-crude oil emulsions, although the precise mechanisms by which they act are not yet fully understood. Being one of the more polar fractions in crude oils, asphaltenes are surface active and strongly adsorb at the oil/water interface, and as the interface becomes densely packed, solid-like mechanical properties emerge, which influence many typical interfacial experiments. The present work focuses on purposefully measuring the rheology in the limit of an insoluble, spread Langmuir monolayer in the absence of adsorption/desorption phenomena. Moreover, the changes in surface tension are deconvoluted from the purely mechanical contribution to the surface stress by experiments with precise interfacial kinematics. Compression “isotherms” are combined with the measurement of both shear and dilatational rheological properties to evaluate the relative contributions of mechanical versus thermodynamic aspects, i.e., to evaluate the “interfacial rheological” versus the standard interfacial activity. The experimental results suggest that asphaltene nanoaggregates are not very efficient in lowering interfacial tension but rather impart significant mechanical stresses. Interestingly, physical aging effects are not observed in the spread layers, contrary to results for adsorbed layers. By further studying asphaltene fractions of different polarity, we investigate whether mere packing effects or strong interactions determine the mechanical response of the dense asphaltene systems as either soft glassy or gel-like responses have been reported. The compressional and rheological data reflect the dense packing, and the behavior is captured well by the soft glassy rheology model, but a more complicated multilayer structure may develop as coverage is increased. Potential implications of the experimental observations on these model and insoluble interfaces for water-in-crude oil emulsion stability are briefly discussed.

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Mesoscopic probes in asphaltenes nanoaggregate structure: from perpendicular to paralleled orientation at the water-in-oil emulsions interface

Abstract: The asphaltenes nanoaggregate structures at water-in-oil emulsions interface were majorly mediated by the molecular weights of the asphaltenes as changed from perpendicular to parallel orientation at the interface with increasing molecular weight.

Cited by 20 publications

References 42 publications

Advances in Asphaltene Petroleomics. Part 4. Compositional Trends of Solubility Subfractions Reveal that Polyfunctional Oxygen-Containing Compounds Drive Asphaltene Chemistry

Advances in Asphaltene Petroleomics. Part 4. Compositional Trends of Solubility Subfractions Reveal that Polyfunctional Oxygen-Containing Compounds Drive Asphaltene Chemistry

Aggregation Behavior of Model Asphaltenes Revealed from Large-Scale Coarse-Grained Molecular Simulations

Assessing the Interfacial Activity of Insoluble Asphaltene Layers: Interfacial Rheology versus Interfacial Tension

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