Characterization of Acidic Compounds in Vacuum Gas Oils and Their Dewaxed Oils by Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry

Abstract

The acidic components in vacuum gas oil (VGO) of cut-2, cut-3, and cut-4 and their corresponding dewaxed oils from a refinery were characterized by negative-ion electrospray ionization (ESI) Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). The acidic heteroatom compounds, N1, N2, N1O1, N1O2, O1, and O2 class species, were identified. Among them, the abundance of O2, O1, and N1 class species were much higher than other acidic class species and characterized by double-bond equivalent (DBE) values and carbon numbers. The N1, N2, N1O1, and N1O2 classes were only identified in VGO cuts instead of dewaxed VGOs. The composition of acidic compounds in VGOs and dewaxed VGOs were correlated with increased boiling point and varied in DBE and carbon numbers. For all identified naphthenic acids, polycyclic naphthenic acids were dominant in VGO cuts, while in their dewaxed oils, naphthenic acids with single-ring were dominant. The most abundant O1 class species had DBE values of 4 corresponding to alkyl phenols in three VGO cuts as well as in three dewaxed VGOs. The abundant N1 class species in three VGO fractions were centered at DBE values of 9 and 12, and these species were likely carbazoles and benzocarbazoles, respectively, while the N1 class species with a DBE of 9 were dominant in three dewaxed VGOs.