Combined Experimental and Computational Study of Polyaromatic Hydrocarbon Aggregation: Isolating the Effect of Attached Functional Groups

Simionesie, Dorin; O’Callaghan, Gregory; Laurent, Raphaël; Preece, Jon A.; Evans, R. Douglas; Zhang, Zhenyu J.

doi:10.1021/acs.iecr.9b04105

Cited by 7 publications

(5 citation statements)

References 83 publications

(151 reference statements)

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“…In this context, controls verify that the computational methods can reproduce experimental results on actual molecules that undergo nanoaggregation in relevant solvents (positive controls) or that do not undergo detectable nanoaggregation (negative controls). Some promising studies of this type are now beginning to emerge . The molecular dynamics studies tend to attempt to validate results by contrasting the behavior of selected molecules in toluene versus the same species in n -heptane.…”

Section: Molecular Basis For Distributed Nanoaggregate Propertiesmentioning

confidence: 99%

“…Some promising studies of this type are now beginning to emerge. 145 The molecular dynamics studies tend to attempt to validate results by contrasting the behavior of selected molecules in toluene versus the same species in n-heptane. This comparison seeks, incorrectly, to represent the phase separation of asphaltenes as an extension of nanoaggregate formation, without verifying the ability of the computational methods to properly represent nanoaggregates in solution at all.…”

Section: Molecular Basis For Distributed Nanoaggregate Propertiesmentioning

confidence: 99%

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Distributed Properties of Asphaltene Nanoaggregates in Crude Oils: A Review

et al. 2021

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The molecules in petroleum asphaltenes follow a molecular structure continuum similar to the rest of the oil but differ in the formation of nanoaggregates in solution. The nature of the aggregation, its size distribution, and dimensions of the nanoaggregates is still debated, and the impact of this aggregation on phase behavior, physical properties, and the processing of heavy petroleum fractions remains unclear. This review first discusses the role of nanoaggregates in the phase separation of asphaltenes, then examines the literature on subfractionation of the asphaltene fraction to define how different molecules partition. Efforts to measure the distribution of nanoaggregate size are summarized, and the roles of size distribution in the behavior of asphaltenes during sedimentation, emulsion formation, and refinery processing are examined. Finally, the molecular basis for formation of a distribution of aggregate sizes/properties is considered. The molecular weight ranges as high as 40,000 Da but the size is below 100 nm. Although few direct experimental data are available for the distribution of aggregate properties, three behaviors indicate the importance of portions of the nanoaggregate population. The highest molecular weight aggregates are the least soluble, driving phase behavior when the asphaltenes are partially precipitated. A portion of these large aggregates are also most responsible for the stabilization of asphaltene films at oil–water interfaces, which stabilize oil-in-water emulsions. The vanadium and nickel species that are most resistant to removal during refining of vacuum residues are also found in the most aggregated fraction, although the stability of the aggregates at process temperatures is not yet proven. Average properties for the asphaltene fraction, including both free molecules and nanoaggregates, are sufficient for prediction of onset of asphaltene phase separation, gravity segregation, and properties such as density and viscosity.

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Section: Molecular Basis For Distributed Nanoaggregate Propertiesmentioning

confidence: 99%

Section: Molecular Basis For Distributed Nanoaggregate Propertiesmentioning

confidence: 99%

Distributed Properties of Asphaltene Nanoaggregates in Crude Oils: A Review

et al. 2021

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“…This methodology was recently used to study the effect of temperature, type of anion and presence of additives onto ion pairing and aggregation of imidazolium‐based ionic liquids as well as for studies of deep eutectic solvents . Similar studies on polyaromatic hydrocarbon aggregation, in particular on the effect of attached functional groups on aggregation, have recently been reported . Additional insights into solvents effects onto molecular dynamics of homogeneous catalytic processes can potentially be obtained by studies of NMR relaxation times.…”

Section: Introductionmentioning

confidence: 99%

Solvent Effects in the Homogeneous Catalytic Reduction of Propionaldehyde with Aluminium Isopropoxide Catalyst: New Insights from PFG NMR and NMR Relaxation Studies

et al. 2020

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Solvent effects in homogeneous catalysis are known to affect catalytic activity. Whilst these effects are often described using qualitative features, such as Kamlet‐Taft parameters, experimental tools able to quantify and reveal in more depth such effects have remained unexplored. In this work, PFG NMR diffusion and T1 relaxation measurements have been carried out to probe solvent effects in the homogeneous catalytic reduction of propionaldehyde to 1‐propanol in the presence of aluminium isopropoxide catalyst. Using data on diffusion coefficients it was possible to estimate trends in aggregation of different solvents. The results show that solvents with a high hydrogen‐bond accepting ability, such as ethers, tend to form larger aggregates, which slow down the molecular dynamics of aldehyde molecules, as also suggested by T1 measurements, and preventing their access to the catalytic sites, which results in the observed decrease of catalytic activity. Conversely, weakly interacting solvents, such as alkanes, do not lead to the formation of such aggregates, hence allowing easy access of the aldehyde molecules to the catalytic sites, resulting in higher catalytic activity. The work reported here is a clear example on how combining traditional catalyst screening in homogeneous catalysis with NMR diffusion and relaxation time measurements can lead to new physico‐chemical insights into such systems by providing data able to quantify aggregation phenomena and molecular dynamics.

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“…They are usually defined as substances that are insoluble in n-heptane but soluble in toluene. 1 The undesired aggregation behavior of asphaltenes can form precipitates that may clog pipelines and damage the petroleum industrial facilities, leading to extensive experimental [2][3][4][5][6] and computational [7][8][9][10] studies on the mechanism of asphaltene aggregation. In general, the aggregation of asphaltenes can be described by the modified-Yen model, 11 in which the asphaltene monomer contains one polyaromatic hydrocarbon (PAH) core with average 6-7 fused aromatic rings and aliphatic side chains, which is also called the "island" structure.…”

Section: Introductionmentioning

confidence: 99%

Data-Driven Insights into the Fluorescence of Asphaltene Aggregates Using Extended Frenkel Exciton Model

Ren,

Liu

2023

Preprint

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The origin of the fluorescence redshift during asphaltene aggregation remains debated due to the great diversity of asphaltene molecules, while the extended Frenkel exciton model provided a theoretical framework for studying multi-chromophore systems such as asphaltene aggregates. We investigated the fluorescence energy of hundreds of asphaltene dimers based on 132 experimentally determined asphaltene monomer structures. Our result shows that the dimer’s fluorescence energy is always lower than both of its monomers regardless of its intermolecular conformation, with its redshift dominated by superexchange. The dimer oscillator strength predominantly depends on the monomer with the lower fluorescence energy, and the involvement of charge-transfer states and the cancellation between monomer transition dipole moments suppressed the fluorescence especially when two monomers have similar fluorescence energy. The above findings hold for all asphaltene dimers despite their diversity, which offers a theoretical interpretation for comprehending the relationship between asphaltene aggregation and its fluorescence variation. Furthermore, this work provides theoretical insights into other research areas related to organic planar conjugated systems with multiple chromophores.

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Combined Experimental and Computational Study of Polyaromatic Hydrocarbon Aggregation: Isolating the Effect of Attached Functional Groups

Cited by 7 publications

References 83 publications

Distributed Properties of Asphaltene Nanoaggregates in Crude Oils: A Review

Distributed Properties of Asphaltene Nanoaggregates in Crude Oils: A Review

Solvent Effects in the Homogeneous Catalytic Reduction of Propionaldehyde with Aluminium Isopropoxide Catalyst: New Insights from PFG NMR and NMR Relaxation Studies

Data-Driven Insights into the Fluorescence of Asphaltene Aggregates Using Extended Frenkel Exciton Model

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