The compositional analysis (speciation) of heavy oil products is a key step to improve our understanding of hydrotreatment processes and reaction mechanisms. Thus, detailed characterization of polar fractions, such as asphaltenes, should be considered. Here, we employ atmospheric pressure photoionization Fourier transform ion cyclotron mass spectrometry to monitor the evolution of the asphaltene hydrocarbon and sulfur families in deep hydrotreatment processes (fixed and ebullated beds). The results suggest that the complexity of the asphaltenic fractions (in terms of chemical polydispersity) is drastically lowered with increased process severity. In either fixed or ebullated beds, the evolution of the sulfur species is quite similar in class composition, aromaticity (DBE/carbon number ratio), and polycondensation (DBE). The compositional changes are marked by a drastic increase in aromaticity to highly polycondensed dealkylated aromatic structures. Asphaltene disaggregation followed by a dealkylation of the remaining species could be suggested. The proposed scheme would converge toward those previously proposed.
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