Structure–Reactivity Relationships for Petroleum Asphaltenes
Murray R. Gray, Martha L. Chacón‐Patiño, Ryan P. Rodgers
Abstract
The role of archipelago asphaltene structure in the reactions of petroleum asphaltenes was investigated by comparing yields of products from the conversion of archipelago-rich heavy oils and bitumen to the yields from a sample with predominant island-type structures. The archipelago content of the asphaltenes was positively correlated with the yield of liquid products boiling below 524 °C. The yield of coke solids increased with the fraction of island structures in the asphaltenes. Furthermore, catalytic hydroconversion of Athabasca bitumen gave a residual asphaltene fraction that was highly enriched in weakly aggregating components, on the basis of extrographic separation, and very low content of archipelago structures. High-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis showed that the heteroatom polydispersity of the asphaltenes after conversion was dramatically reduced, and the range of double-bond equivalents and carbon number was close to the limiting boundary of planar polynuclear aromatic hydrocarbons (PAHs). The radical cations from the converted asphaltenes showed significant concentration of high-ring-number/known PAH structures. The results highlight the existence of a positive correlation between the amount of archipelago structural motifs in asphaltenes and the yield of products with a range of boiling points below 524 °C. Moreover, the data demonstrates that advanced hydroconversion methods can be used to obtain asphaltene fractions with decreased polydispersity in terms of heteroatom content, alkyl-substitution, and molecular structure, which could be eventually exploited for material science applications.