Distribution of Ni and V in A1 and A2 Asphaltene Fractions in Stable and Unstable Venezuelan Crude Oils

Asphaltenes are a complex mixture of compounds grouped as the colloidal phase in crude oils. Two fractions, A1 and A2, have been isolated from them. A1 is defined as the mayor and practically insoluble fraction, while A2 has a similar solubility to the original asphaltenes in toluene. The studies on the molecular structure, organic compound distribution, and metal content can help to better understand the chemical behavior of these two fractions. In this sense, the concentration of Ni and V and elemental analysis (C, H, N, and S) were determined in asphaltenes and their fractions. The samples were analyzed using inductively coupled plasma atomic emission spectrometry and elemental combustion analysis. Results show that A1 presents higher Ni and V concentrations than A2, in both stable and unstable crude oils. These results can be explained by strong interactions, such as covalent bonds between the petroporphyrins and the asphaltene molecules. V/V + Ni ratios suggest differences in the distribution of metallo compounds between A1 and A2. Finally, organic elemental analysis ratios suggest variations in the aromatic character of both asphaltene fractions.