Characterization of compositional changes in vacuum gas oil distillation cuts by electrospray ionization Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry

We present the acidic polar heteroatomic molecular class composition of three distillate fractions (light, 563-606 °F; middle, 606-853 °F; and heavy, 853-1009 °F) of a vacuum gas oil (VGO). Acidic and basic species were detected by high-resolution negative-ion and positive-ion electrospray ionization (ESI) Fourier transform - ion cyclotron resonance mass spectrometry (FT - ICR MS). Each distillate was exhaustively characterized by mass, heteroatom class, type (rings plus double bonds), and carbon number distribution to mark compositional trends with increased distillation temperature. The light distillate fraction exhibits monoaromatic and low double-bond equivalence (DBE) polycyclic species. Low-molecular-weight polycyclic and monoaromatic carboxylic acids and oxygen - sulfur (S_xO_y) species solely populate the negative-ion mass spectrum of the light distillate. In contrast, the middle and heavy distillates are composed of high-molecular-weight and high-DBE polyaromatic species such as pyrrolic and phenolic species, in addition to polyaromatic carboxylic acids. Light and middle distillate carboxylic acids and O_xS species fractionate by alkyl chain length but not by DBE value.