Advances in Asphaltene Petroleomics. Part 3. Dominance of Island or Archipelago Structural Motif Is Sample Dependent

Abstract

Asphaltene structure is one of the most controversial topics in petroleum chemistry. The controversy is centered on the organization of aromatic cores within asphaltene molecules (single aromatic core, island and multiple aromatic core, archipelago) and specifically the inconsistency between the island model and the composition of the products derived from asphaltene pyrolysis/thermal cracking. Such products are consistent with the coexistence of island and archipelago asphaltene structural motifs. However, the archipelago model continues to lack the widespread acceptance of the petroleum community, in part due to mass spectrometry results in support of the island model. In the first and second part of this series, we demonstrated that the disproportionally high atmospheric pressure photoionization (APPI) ionization efficiency (monomer ion yield) of island species is due to weak nanoaggregation of large aromatic cores which do not extensively aggregate in toluene, whereas more archipelago-dominant fractions were shown to have low monomer ion yield due to a greater propensity for aggregation. The discrepancy leads to bias toward the selective ionization of island compounds and thus the erroneous mass spectrometry support of the predominance of the island structural model. A separation method based on aggregation trends and therefore the efficiency of monomeric ion production is critical to access archipelago structures. In the work presented herein, we demonstrate that dominance of island or archipelago structural motif is sample dependent. We present the positive-ion APPI Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) characterization of asphaltenes and asphaltene extrography fractions derived from Wyoming Deposit (island dominant) and Athabasca Bitumen (archipelago dominant) C7 asphaltenes. Wyoming Deposit asphaltenes resemble the “classical” island-type asphaltene structure: they exhibit a high concentration of highly aromatic/alkyl-deficient species with a compositional space close to the polycyclic aromatic hydrocarbon (PAH) limit. Fragmentation results from infrared multiphoton dissociation (IRMPD) confirm that island is the dominant structural motif in Wyoming Deposit C7 asphaltenes; the predominant fragmentation pathway for all extrography fractions consists of loss of CH2 units (or dealkylation), without significant loss of aromaticity. Conversely, Athabasca Bitumen C7 asphaltenes exhibit an “atypical” molecular composition. More than 40 wt % of the sample is extracted in the latest extrography fractions, which are composed of difficult-to-ionize species, a fraction of which exhibit atypically low double bond equivalent (DBE = 5–12) and extended homologous series with carbon numbers up to 60. The fragmentation behavior of all Athabasca Bitumen-derived fractions demonstrates a predominant contribution of archipelago motifs. Our results suggest that the Yen-Mullins molecular definition of asphaltenes cannot be used to describe all asphaltene samples. Island and archipelago structura...

Investigation of Island/Single-Core- and Archipelago/Multicore-Enriched Asphaltenes and Their Solubility Fractions by Thermal Analysis Coupled with High-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…[48,49] The predominance of both structures not only depends on the regarded fraction but also on the origin of the asphaltenes as well as the investigated molecular mass range. [50] In a recent study, Athabasca bitumen and Wyoming deposit asphaltenes were investigated by APPI-IRMPD-FT-ICR MS. While Athabasca asphaltenes revealed dominant island-and archipelago-like fragmentation throughout the mass range, Wyoming asphaltenes revealed dominant island-like fragmentation for smaller molecular weight asphaltenes, whereas higher m/z-values exhibited both structural fragmentation pathways.…”

Catalogue of Plausible Molecular Models for the Molecular Dynamics of Asphaltenes and Resins Obtained from Quantitative Molecular Representation

“…13 The most recent comprehensive characterizations performed using extrographic fractionation and ultrahigh-resolution mass spectrometry seem to indicate that, as one would expect, asphaltenes comprise a structural continuum of both continental (island) and archipelago motifs. 14,15,16 In this scenario, not surprisingly, the theoretical descriptions lag behind. Any equation-of-state modelling of asphaltene phase behavior and/or deposition process will invariably suffer from the lack of an appropriate description of what, in essence, is a continuous molecular distribution, and as such, current models struggle to provide quantitative predictions.…”

Mechanistic Approach to Thermal Production of New Materials from Asphaltenes of Castilla Crude Oil

“…Li & Greenfield [8] recommended retaining the overall architecture, whereas the location of several side groups was changed to restore the planarity of the aromatic rings. Recently, new findings [9] support the idea of a macromolecule consistent with the existence of both kinds of models. The ratios of the archipelago and island structures depended on the asphaltene origin [7].…”