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

Despite extensive research, the molecular-level chemical characterization of asphaltenes, a highly aromatic solubility fraction of petroleum, remains an analytical challenge. This fraction is related to diverse problems in crude oil exploration, transportation, and refining. Two asphaltene architecture motifs are commonly discussed in literature, “island” (single core) and “archipelago” (multicore) type structures. The thermal desorption and pyrolysis behavior of island- and archipelago-enriched as-phaltenes and their extrography fractions was investigated. For this purpose, the evolved chemical pattern was investigated by thermal analysis coupled to ultrahigh resolution mass spectrometry (FT-ICR MS). Soft atmospheric pressure chemical ionization preserved the molecular information of the thermal emission profile. Time/temperature-resolved analysis allowed the chemical characterization of occluded material as well as of asphaltene building blocks during pyrolysis.

Regarding the thermogravimetric information, the island-type enriched sample (Wyoming asphal-tenes) revealed a significantly higher coke residue after the pyrolysis process compared to the archi-pelago-type enriched sample (Athabasca asphaltenes). In contrast to whole asphaltenes, extrograph-ic fractions revealed occluded material evolved during the desorption phase. For the acetone frac-tion, this effect was most abundant and suggests cooperative aggregation.

Pyrolysis revealed a bimodal behavior for most of the compound classes suggesting the presence of both architecture motifs in each asphaltene. DBE versus #C diagrams of the pyrolysis molecular pro-file revealed specific compositional trends: compounds with high DBE values and short alkylation likely to be originated from island-type asphaltenes, whereas species with low DBE values and high carbon numbers likely derive from archipelago-type asphaltenes.

In the asphaltene structural debate, thermal analysis ultrahigh resolution mass spectrometry serves as additional technique and supplements results obtainable by other techniques, such as direct infu-sion approaches. Consistent results on the structural motifs are indicated by the molecular finger-print visualized by DBE versus #C diagrams and serve as measure for the dominance of a structural motif.