Vanadium and nickel distributions in Pentane, In-between C5-C7 Asphaltenes, and heptane asphaltenes of heavy crude oils

Abstract After selective solvent extraction, the volatile and non-volatile vanadium and nickel distributions for two Venezuelan heavy crude oils and the NIST Standard Reference Material SRM 8505 were determined for the Entrained n-pentane (C5) maltenes, In-between C5-C7 asphaltenes, and n-heptane asphaltenes. The fractions were analyzed via the asphaltene solubility profile, size exclusion chromatography (SEC), High-Temperature Gas Chromatography coupled with Inductively Coupled Plasma Mass Spectrometry (HTGC-ICP-MS), and atmospheric pressure photoionization Fourier-transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS). Results showed that petroleum elution is strongly correlated to high hydrogen deficiency and increased heteroatom levels. The solubility decreased in the following order: Entrained C5 Maltenes, In-between C5-C7 asphaltenes, and C7 asphaltenes. Qualitative HTGC-ICP-MS shows that 51V traces of the first two asphaltene fractions showed a bimodal (Venezuelan crude oil 1 and NIST SRM 8505) or a multimodal distribution (Venezuelan crude oil 2). On the other hand, the 51V signal intensities for C7 asphaltenes were the lowest among all samples studied. FT-ICR MS revealed that the chemistry of vanadyl and nickel porphyrins is multimodal in terms of DBE. N4O1V1 and N4O2V1 classes exhibited abundant homologous series with DBE values of ≤22; when sulfur was incorporated, e.g., N4O1S1V1 class, the DBE increased by 4–6 units. Ni-containing porphyrins showed two major homologous series, pointing toward a bimodal chemical nature. We hypothesized that this compositional feature could be why the bimodal and multimodal distributions of boiling points were found in the studied heavy crude oil fractions.