Characterization of Basic Nitrogen Species in Coker Gas Oils by Positive-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Abstract

Six coker gas oils (CGOs) and three basic fractions extracted from one of the CGOs by 0.1, 0.4, and 1 M HCl hydrochloric acid were characterized by positive-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) and compared to those analyzed by gas chromatography mass spectrometry (GC-MS). The ultra high mass resolving power and high mass accuracy of FT-ICR MS allow the assignment of a unique elemental composition to each peak in the mass spectrum. Basic nitrogen species were characterized by class, type, and carbon number. The mass spectra of the CGOs at the 200−500 Da mass range were similar, but the distribution of double bond equivalence (DBE) versus carbon number were different. Among the N, N2, NO, and NS that were identified in CGOs, the N class nitrogen species were dominant. The results showed that hydrotreating reduced the relative abundance of all class species, except for the N class species. This suggests that some N class species are refractory to hydrotreating. The molecular weight of nitrogen species in the acid-extracted basic nitrogen fraction of CGO was lower than that of its parent CGO. The N3, NO2, and N2O class species were clearly identified and concentrated in the basic nitrogen fraction, but were not detected in their parent CGO. The N class species with ring plus DBE value of 4−16 in the basic nitrogen fraction were also identified by GC-MS analysis.