Structure Elucidation and Sulfur Species Characterization of Asphaltenes Derived from Heavy Fuel Oil Using APPI (+) and ESI (+) FT-ICR Mass Spectrometry

Asphaltenes are the most complex and the least understood portions of heavy oils. In the current study, a powerful tool Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with positive atmospheric pressure photoionization (APPI) and positive electrospray ionization (ESI) ionizers was used, respectively, to analyze and understand the nonpolar parts and the polar parts of the asphaltenes obtained from Saudi Arabian heavy oil. APPI (+) FT-ICR MS analysis confirmed 9529 different molecular structures having average molecular weight (AMW) of 582.6 Da. Hydrocarbon parts and individual sulfur molecular classes of asphaltenes were categorized into sub-classes. The relative abundance of the hydrocarbon parts (mostly aromatic) and individual sulfur molecular classes were approximately 30.61% and 31.59%, respectively. ESI (+) FT-ICR MS analysis confirmed 3151 distinct molecular structures with AMW of 518.2 Da. The relative abundance of the individual nitrogen (N) was approximately 42.71%. Asphaltene average molecular structure was predicted as C_39.09H_54.04S_0.6N_0.16O_0.07 based on the APPI (+) and ESI (+) FT-ICR MS analyses and Van Krevelen diagrams. It also confirmed the presence of both the island model and Archipelago model structures in the surrogated asphaltene molecule.