Relationship between aromatic hydrogen and aromatic carbon in straight run and converted oils

In the conversion of high boiling oil fractions, it is difficult to track compositional changes that affect the chemical nature of species. For reaction engineering, monitoring changes related to hydrogen transfer reactions and formation of aromatic species as thermal conversion progresses to coking is useful. Proton and carbon-13 nuclear magnetic resonance (H-1 and C-13 NMR) spectrometry can measure the aromatic hydrogen and aro-matic carbon content in oils of diverse origin and distillation range. C-13 NMR analyses are more time consuming than H-1 NMR analyses. The ability to calculate the aromatic carbon content of oils directly from measured ar-omatic hydrogen content is alluring and is reportedly feasible (Cookson, et al. Fuel 1986; 65:1247-1253). In this work previously reported H-1 and C-13 NMR data for different petroleum and coal derived oils were collated and supplemented with experimental measurements that included narrow cuts of straight run and refined oils, as well as bitumen-derived mixtures that were thermally converted at different levels of severity. It was found that aromatic carbon content, C-Ar, was only broadly related to aromatic hydrogen content, H-Ar. A wide range of values for C-Ar was possible for a specific value of H-Ar. The medium atmospheric equivalent boiling point tem-perature, T-50, was a poor descriptor for indicating a directional change in the relationship between C-Ar and H-Ar, both for wide and narrow boiling range distillation fractions. An increase in heterocyclic aromatic content caused a decrease in the (H/C)(Ar) ratio, since heteroatoms in aromatics are mainly found in ring-edge and not in ring -junction positions. When the changes in H-Ar and C-Ar of different bitumen-derived materials with respect to thermal conversion severity were evaluated, it was found that changes in H-Ar and C-Ar were not in a fixed relation to each other.

Automated summary

It is difficult to track compositional changes that affect the chemical nature of species during the conversion of high boiling oil fractions. Proton and carbon-13 nuclear magnetic resonance (H-1 and C-13 NMR) spectrometry can measure the aromatic hydrogen and aromatic carbon content in oils. There is only a rough correlation between aromatic carbon content and aromatic hydrogen content.