Characterization and Structural Classification of Heteroatom Components of Vacuum-Residue-Derived Asphaltenes Using APPI (+) FT-ICR Mass Spectrometry

Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been widely used as a major breakthrough to investigate the structure of asphaltenes in heavy oils. In this study, saturates, aromatics, resins, and asphaltenes (SARA) fractions derived from vacuum residue were analyzed using FT-ICR MS, and, particularly, the asphaltenes were examined in detail. Basically, the mass-to-charge ratio spectra, double bond equivalents (DBE) distribution, and heteroatom classes of SARA fractions were checked. After that, we delved into the asphaltenes with very high aromaticity and classified the asphaltenes according to heteroatom classes to understand their structural diversity. This classification disclosed that the DBE distribution of asphaltenes exhibited different trends, depending on heteroatom classes and the number of heteroatoms, which could not be identified by DBE distribution of whole asphaltenes. Based on the relative abundance peaks of the DBE and carbon number distribution, the compositional space of DBE and carbon number was separated into four groups in various heteroatom classes. The structure types of asphaltenes corresponding to each group are maltene-like components (DBE 5-15, carbon number 20-60), archipelago-type asphaltenes (DBE 10-25, carbon number 25-70), island-type asphaltenes (DBE 15-35, carbon number 25-60), and larger island-type asphaltenes (DBE 35-50, carbon number 40-75), which are highly aromatic and independent of the normal island-type asphaltenes. The classification results are expected to be applied to develop a structural model of asphaltenes.