Three crude oils were employed for precipitation of asphaltenes using two solvents, n-pentane and n-heptane. Crude oils were analyzed by API gravity, elemental composition and metals content. Asphaltenes were characterized by VPO molecular weight, liquid State 1H and 13C NMR, elemental composition, and metals content. Spectra were divided in three and two different regions for 1H and 13C NMR, respectively, to determine the most important structural parameters of asphaltenes. To avoid errors when determining asphaltene content and characterization, a solvent-to-oil (S/O) ratio of 60:1 was used. This optimal ratio was defined after conducting various experiments with different values of S/O in the range of 5:1 to 100:1. It was found that solvent type has a very important influence in composition of asphaltenes, which were also very different for the three crude oils studied. Aromaticity of asphaltenes was higher when n-heptane was employed.

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Precipitation with n-heptane and characterization of asphaltenes were carried out for products obtained during hydrotreating of Maya heavy crude oil. Hydrotreating experiments were conducted in a pilot plant at constant pressure, hydrogen-to-oil ratio, and space-velocity. Reaction temperature was varied in the range of 380-440 °C. Maya crude and hydrotreated products were characterized by API gravity and sulfur, nitrogen, nickel, vanadium, and asphaltenes contents. Elemental analysis, metals content, VPO apparent molecular weight, and NMR measurements were performed in the asphaltenes fraction. The effects of reaction temperature on asphaltenes properties during hydrotreating are discussed in terms of changes in heteroatoms contents and structural parameters.