Characterization of basic nitrogen species in coker gas oils by positive-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Quan Shi,^*,† Chunming Xu,^† Suoqi Zhao,^† Keng H. Chung,^‡ Yahe Zhang,^† and Wei Gao^†

^†State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, People’s Republic of China, and^‡Department of Chemical and Petroleum Engineering, The University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada

Corresponding Author: Email: sq@cup.edu.cn

DOI: 10.1021/ef9008983

Keywords: Ionization; ions; Mathematical methods; Nitrogen; Nitrogen compounds

Abstract: Six coker gas oils (CGOs) and three basic fractions extracted from one of the CGOs by 0.1, 0.4, and 1 M HCI 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.