Effect of Thermal and Initiated Cracking on the Structure of HighMolecular-Weight Heteroatomic Components of Atmospheric Residues. Part 1: Asphaltenes

Abstract Using scanning electron microscopy, Fourier transform infrared spectroscopy, structural group analysis, and chemical degradation of carbon–heteroatom bonds, this study presents a comparative macro- and microstructural examination of asphaltenes. The asphaltenes were isolated from a crude oil atmospheric residue from the Krapivinskoye field, as well as from liquids produced by thermal cracking and fly-ash-ferrosphere-initiated cracking of this residue. Asphaltenes obtained from the original atmospheric residue and its cracking products are predominantly amorphous. During cracking, the structural units of asphaltenes become more compact, mainly due to a reduction in the number of naphthenic rings within the polycyclic system. In asphaltenes from thermal cracking, the paraffin carbon atoms form short alkyl substituents, while in those from initiated cracking, they predominantly form long alkyl chains that are either linear or slightly branched. In the liquid products resulting from the chemical degradation of C–S and C–O bonds in the asphaltene macromolecules, compositionally similar nalkanes, hopanes, phenylalkanes, and ethyl nalkanoates were identified across all samples (the original residue and the products of both cracking processes). Among the Slinked fragments in the asphaltene macromolecules from thermal and initiated cracking, even-carbon-numbered nalk-1-enes were additionally detected. The introduction of a cracking additive was found to deepen asphaltene degradation at both the macro- and micromolecular levels. This is attributed to the intensification of aromatic ring condensation, the cracking of naphthenic rings in naphthene–aromatic fragments, the cracking of the resulting paraffinic chains, and the cleavage of C–S and C–O in aliphatic substituents attached to aromatic rings and in bridges linking aromatic units.