Abstract
The structure of asphaltene is an important factor in the reactivity of heavy hydrocarbons, with. elemental analysis and nuclear magnetic resonance (NMR) spectrometry commonly used to evaluate its structure. However, such analyses can be limited by small sample amounts. In particular, 13C-NMR for the determination of carbon aromaticity (fa) requires about 100 mg of asphaltene, whereas elemental analysis and 1H-NMR need only 10 mg or less. In addition, 13C-NMR has the disadvantage of a long time. To avoid these drawbacks, we used a statistical estimation method to determine the fa of the pentane-insoluble and hepane-soluble fraction (C5AS) based on the results of elemental analysis and 1H-NMR analysis using 29 worldwide vacuum resides. Results showed that the fa was estimated within an error of 0.03 using H/C, N/C and S/C atomic ratios obtained by an elemental analysis, and hydrogen distribution obtained by 1H-NMR. The difference between the observed and estimated number of aromatic rings per unit structure was expected to be within 1. This method can estimate the fa for C5AS using a sample of only 20-30 mg, and the structural analysis is more accurate than that without fa value.
