Alkyl Side Chains Connected to Aromatic Units in Dagang Vacuum Residue and Its Supercritical Fluid Extraction and Fractions (SFEFs)

Dagang vacuum residue (VR) was separated into 16 extractable fractions and a non-extractable end cut by the supercritical fluid extraction and fraction (SFEF) technique. The average molecular structures of the VR and selected SFEFs were determined. The VR and SFEFs were further separated into saturate, aromatic, resin, and asphaltene (SARA) subfractions. Aromatic, resin, and asphaltene subfraction were subjected to ruthenium-ion-catalyzed oxidation (RICO). A homologous series of n-alkanoic acids and α,ω-di-n-alkanoic acids have been detected and measured in the reaction product after esterification with diazomethane or phenacyl bromide. Concentrations of n-alkanoic acids (C1−C33) were determined, which indicated the content distribution of n-alkyl side chains attached on aromatic carbon. Those α,ω-di-n-alkanoic acids (C4−C26) represented polymethylene bridges, connecting two aromatic units in the sample. This information was unavailable in average molecular structure analysis.