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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 most abundant metals in heavy feedstocks, vanadium and nickel, are mainly concentrated in the asphaltenes fraction, a petroleum fraction which precipitates in presence of paraffinic solvents. Characterization of vanadium and nickel complexes is therefore important to the development of demetallation and conversion strategies used to process heavy crudes. The dependence of vanadyl structures on the geographic origin of feedstocks and their evolution during hydroprocessing in an ebullated-bed pilot unit were studied. The aim of this contribution is to assess the possibilities of the EPR spectroscopy to provide information on the structure of the vanadyl species. This work shows that pulsed EPR spectroscopy is a powerful technique that allows to distinguish several types of environments of vanadium species, amongst which are porphyrinic ligands, even in very complex samples such as C 7 asphaltenes from heavy feedstocks.

Heavy oil fractions can be upgraded through various processes, such as catalytic residue hydrotreatments. Mass transfer of macromolecules present in the heavy oil fraction, so-called asphaltenes, from feedstock to catalytic active sites is limited during hydroprocesses. Mechanisms of the diffusion of asphaltenes through pore network, adsorption, and pore plugging are no well-known under process conditions. A new method has been developed to characterize and investigate asphaltene diffusion phenomenon in catalysts under a high temperature and pressure. Alumina supports immersed in asphaltene solution are left to evolve at 250 °C and 5.0 MPa. Solutions and supports are analyzed to quantify the mass transfer, penetration depth, and change in support porosity of asphaltenes. This procedure was evaluated in terms of reproducibility and sensitivity. The impact of several parameters, such as pressure, was appraised. With this powerful procedure, for the first time, asphaltene diffusion without conversion into the pore network of a catalyst at a high temperature and pressure has been monitored over time. In accordance with analytical results, we proposed a primary model for the asphaltene adsorption and pore network cluttering mechanism under hydroprocessing conditions.