Preliminary studies of asphaltene aggregates by low vacuum scanning electron microscopy

A study of vacuum residue and asphaltenes from a Mexican oil refinery was performed using low vacuum scanning electron microscopy (LV-SEM) to determine the morphology of aggregates, and energy dispersive spectroscopy (EDS) to get the elemental composition of them. Irregular shaped particles were observed on vacuum residue, with a size range from 10 to 30 mum, that emerged from the oily fraction under the action of the electron beam. Those particles were sulphur and silicon rich. We also found some particles with important concentrations of Mg, Cl, K, and Fe. Asphaltenes precipitated with different n-alkane solvents showed slight differences in morphology. Fragile particles of several sizes were analyzed (230 x 130 mum to 730 x 240 mum); most of them presented a smooth face side by side with a rough one. Higher magnification of the smooth faces showed some randomly distributed pores. Rough facets tended to show larger pores. Some inclusions were also found; the sizes of those ranged from 7 to 25 mum EDS revealed that sulphur and silicon are more abundant in the inclusions. Some Fe and Mg rich particles were also found. All the samples presented small amounts of V, and some of them Zn and Sn, whose concentration depends on the solvent used.