Size exclusion chromatography: Characterization of heavy petroleum residues. application to resid desulfurization process

Size exclusion chromatography (SEC) is still the only of the existing analytical methods that can easily and routinely provide information on relative asphaltene molecular weight distributions. However, molecular weight characterization still suffers from several physicochemical drawbacks such as association Of Molecular units, adsorption on column material and lack of appropriate standards, which are not always underlined in the petrochemical literature where SEC is used Lis a routine analytical tool. Thus, the resulting molecular weight distribution can be either overestimated or underestimated depending on the chosen experimental conditions: sample concentration, solvent, temperature, type of column packing. In order to further reduce these artefacts, the influence of the above operating parameters has been studied on Arabian petroleum asphaltenes. Our results show that the obtained bimodal profiles are mainly due to association-dissociation phenomena rather than the co-existence of two distinct molecular populations of low and high molecular weights. Based on these results, samples from pilot plants were studied. We will show that SEC enables to differentiate asphaltenes from different source rocks and to follow feed and effluent evolutions during hydroconversion process. Even though this technique should be only used on a relative basis to compare molecular weight distributions at given analytical conditions, it was revealed to be very useful for the understanding of main hydroconversion reaction pathways.