The size distribution of sulfur, vanadium, and nickel was determined for four crude oils and their distillation cuts using gel permeation chromatography (GPC) coupled to inductively coupled plasma high-resolution mass spectrometry (ICP HR MS). The results show a trimodal distribution of vanadium and nickel compounds in the crude oils, the atmospheric residues, and the vacuum residues and, for sulfur compounds, either a mono- or bimodal distribution depending upon the distillation cut considered. A correlation exists between the sulfur fraction retention times and the temperature cuts of the distillation for a temperature below 560 °C and also between the viscosity of the crude oils and the proportion of trapped sulfur compounds in a higher boiling temperature fraction. The thermic treatment applied for the distillation increases the aggregation of low- and medium-molecular-weight compounds of vanadium and nickel into higher molecular weight aggregates between the crude oil on the one hand and the atmospheric residue and vacuum residue on the other hand, especially when the crude oil has a high total sulfur content.

Gel Permeation Chromatography Inductively Coupled Plasma High Resolution Mass Spectrometry (GPC ICP HR MS) was used for the understanding of the evolution of two crude oil cut samples after their dilution. We firstly studied different method parameters in order to compare two GPC procedures already published (flow rate, column set, presence or not of the THF stabilizer). Thus, the principal parameters affecting the molecular size distribution and its evolution were demonstrated. The column set and flow rate can affect drastically the molecular size distribution of the sample. Moreover an evolution of the size distribution of the complexes of vanadium, nickel and sulfur into higher molecular weight compounds was observed over time.The study led to the recommendation of the sample preparation to the same day of the analysis in order to obtain reproducible data.

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The objective of this work was to separate and study a least stable fraction of Hassi−Messaoud asphaltenes that flocculate during oil transport and storage. The unstable fraction was studied by consecutive fractioning with solvents differing in polarity. A correlation between structural parameters of asphaltenes and the flocculation onset was established. It was demonstrated that the spontaneously flocculating part of asphaltenes is composed of relatively small molecules that are less aromatic and contain more heteroatoms than more stable asphaltenes. The length of the side aliphatic chain was shown to be an important parameter influencing the flocculation onset.