Extraction and characterization of asphaltenes from different crude oils and solvents

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 H-1 and C-13 NMR, elemental composition, and metals content. Spectra were divided in three and two different regions for H-1 and C-13 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.