NMR determination of petroleum asphaltenes and their model molecules evaluation

~1H and~(13)C NMR spectra of 6 petroleum asphaltenes, separated from different crude oils with n-hexane as solvent, were determined with a Bruker Avance DMX500 NMR spectrometer. And then a series of average chemical structural parameters were obtained. By combining the relative molecular weight and the elemental analysis results, the average molecular formula of the asphaltene units was calculated and the model molecules were evaluated. It is found that the asphaltene units are mainly composed of polycyclic aromatics linked with naphthene rings, side aliphatic chains, and O, N and S atoms. The asphaltene units are associated each other with the association number about from 4 to 6. These results provide an efficient structural description for the further study of petroleum asphaltenes at molecular level.