Characterization of Heteroatom Compounds in a Crude Oil and Its Saturates, Aromatics, Resins, and Asphaltenes (SARA) and Non-basic Nitrogen Fractions Analyzed by Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Abstract

A Liaohe crude oil was separated as saturates, aromatics, resins, and asphaltenes (SARA) and neutral nitrogen fractions. The crude oil and its subfractions were analyzed by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results show that neutral nitrogen and acidic heteroatom compounds in the crude oil contain 15−55 carbon atoms with double-bond equivalent (DBE) values of 1−27, containing N 1, N 2, N 1 O 1, N 1 O 2, N 1 O 3, N 1 O 4, O 1, and O 2 heteroatom classes. No molecules in the saturate fraction can be ionized by ESI. The aromatic fraction contains N 1 and N 1 O x compounds with high molecular weights but low DBE values. The resin and asphaltene fractions contain highly aromatic and acidic class species, which are enriched in oxygen- and nitrogen-containing compounds with lower molecular weights than those found in the aromatic fraction. The distribution patterns of N 1, N 1 O 1, and O 1 class species in the resins and asphaltenes are similar. The mass spectrum of the neutral nitrogen fraction differs from those for the bulk crude oil and its SARA fractions; the neutral nitrogen fraction is enriched with N 1 and N 1 O 1 class species. Neutral nitrogen compounds with molecular weights lower than 200 were discriminated in the FT-ICR MS spectrum under the chosen operating conditions. However, the nitrogen species detected by gas chromatography only accounted for a small amount of that found in the neutral nitrogen fractions. Some of the neutral nitrogen species were entrained in asphaltenes during the deasphalting step of sample fractionation.