Characterization of Nitrogen Compounds in Coker Heavy Gas Oil and Its Subfractions by Liquid Chromatographic Separation Followed by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Abstract

A coker heavy gas oil (CHGO) was separated into saturates, aromatics, resins, and asphaltenes (SARA) fractions. The resin fraction was separated into six subfractions by high-performance liquid chromatography (HPLC). The CHGO and its subfractions were characterized by electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The mass spectra showed that the mass range of basic and neutral nitrogen compounds was 200−450 and 160−400 Da, respectively. Five nitrogen class species, N1, N2, N1O1, N1O2, and N1S1, were assigned in the positive-ion spectrum. Six nitrogen class species, N1, N2, N1O1, N1O2, N2O1, and N1S1, were assigned in the negative-ion spectrum. Among the identified nitrogen compounds, the N1 class species was dominant. The N1 class species were enriched in the resin fraction. The N2 class species are likely amphoteric molecules and were enriched in the asphaltene fraction. The composition of nitrogen compounds in the resin subfractions varied significantly in double-bond equivalence (DBE) and carbon number. As the polarity of the resin subfraction increased, the average molecular weights of the nitrogen compounds decreased, DBE values for each heteroatom class species increased, and the N2 class species became the dominant nitrogen compounds at the expense of the N1 class species.