Characterization of asphaltenes from Cold Lake heavy oil: variations in chemical structure and composition with molecular size

Asphaltenes from Cold Lake oil were separated into fractions by size exclusion chromatography to study the molecular size dependence of chemical structural characteristics. Each fraction was analyzed by proton NMR and UV-visible spectroscopy and by elemental analyses for C, H, N, S, Ni, and V. The results indicated that the nature of the average chemical structures in Cold Lake asphaltenes were not uniform throughout the total range of molecular sizes but varied significantly; some changed gradually and some changed quite abruptly. Especially in the very low molecular-weight fraction, the size of aromatic moieties seems to be much smaller, the contents of both aromatic carbon and aromatic hydrogen are higher, the C/H ratio is higher, and the porphyrin and vanadium concentrations are much higher than in heavier fractions. Keywords: Cold Lake asphaltenes, size fractionation, vanadium, proton NMR, porphyrin, chemical structural analysis.