Narrow distillation cuts for an improved characterisation of crude oil: an insight on heteroatoms in heavy fraction molecules

A light Arabian crude oil was separated by distillation into 27 fractions, including 25 very narrow distillation cuts, the light ends, and a vacuum residue (VR), which were extensively characterised using standard methods. Overall, the properties matched well with those predicted by H/CAMS software, indicating a successful distillation. Then, quantitative C-13 NMR spectroscopy, SIMDIS, and molecular weight (MW) distribution by mass spectrometry were used to derive an improved correlation between the MW and boiling point for the entire crude oil, in particular for the VR fraction. This allowed determining the mass fractions of sulphur and nitrogen containing compounds across the crude oil boiling range, reaching up to approximately 100% in the VR fraction. The corresponding low abundance of pure hydrocarbon molecules in the VR fraction is important for modelling purposes and processing technologies.