The definition of asphaltenes as highly aromatic/alkyl-deficient compounds enriched in single-core motifs (“island”), in which aggregation is exclusively driven by π-stacking interactions, has persisted in the literature for over five decades. Classical asphaltene science excludes the central role of both heteroatom-based interactions (<i>i.e.,</i> hydrogen bonding) and multi-core (“archipelago”) motifs in asphaltene aggregation, which is inconsistent with known asphaltene behavior in thermal cracking and emulsion stabilization. To determine whether or not heteroatoms and/or archipelago motifs are critical for behaviors such as aggregation, cracking, and emulsion stability, we have developed fractionation methods that enable asphaltene separation based on structural motifs, heteroatom content, and interfacial activity. The results demonstrate that island and archipelago motifs coexist in a structural continuum, and the dominance of archipelago structures is sample-dependent and correlates with strong aggregation trends, production of 1-5 ring aromatics in cracking processes, and pronounced emulsion aging/stabilization. For the first time, we offer conclusive evidence for the existence of atypical asphaltene species with low aromaticity and high levels of oxygenated functionalities. These atypical compounds are interfacially active, reside in the most insoluble asphaltene subfractions due to their high heteroatom content, and exhibit an ionization behavior that suggests the predominance of hydrogen-bonding interactions in solution. Furthermore, asphaltene irradiation in a solar simulator that mimics oil weathering after spills demonstrates behavior consistent with refinery applications: upon oxidation, archipelago motifs yield abundant water-soluble species with lower carbon number/lower aromaticity, whereas island compounds do not. Collectively, the results highlight the need for an asphaltene molecular model that acknowledges the critical role of strong intermolecular forces such as hydrogen bonding and the coexistence of island/archipelago motifs and classical/atypical asphaltene species.

Towards a new molecular description of asphaltenes by fourier transform ion cyclotron resonance mass spectrometry

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.