アスファルテンの炭素芳香族性の元素分析およびプロトンNMRからの予測

抄録

The structure of asphaltene is an important factor for investigating the reactivity of heavy hydrocarbons. For the evaluation of asphaltene, elemental analysis and NMR analysis are commonly applied. However, such analyses are sometimes limited due to too small sample size. Especially, ¹³C-NMR analysis for the determination of carbon aromaticity (fa) requires about 100mg of asphaltene while elemental analysis and ¹H-NMR analysis requires only 10mg or less. In addition, ¹³C-NMR analysis takes quite a long time for the measurement. It is well known that H/C atomic ratio has a strong relationship with fa, but it has relatively weak relationship with molecular structure. Therefore, we studied a statistical estimation method for fa of hepane-insolubles (asphaltene) from the results of elemental analysis and 1H-NMR analysis using 45 worldwide vacuum resides (VR). As a result, fa was estimated within a error of 0.04 using H/C, N/C, S/C and O/C atomic ratios obtained by an elemental analysis and hydrogen distribution obtained by ¹H-NMR. The difference between observed number of aromatic rings per unit structure and estimated ones is within one. Those results are quite effective because only 20-30 mg of samples are necessary to obtain fa, and the data set for the average molecular structure analysis can be obtained from very small sample size obtained by a preparative GPC, for example.