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

Quan Shi, Dujie Hou, Keng H. Chung, Chunming Xu,*, Suoqi Zhao, and Yahe Zhang

Quan Shi - State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102200, People’s Republic of China

Dujie Hou - Faculty of Energy Resources, China University of Geosciences, Beijing 100083, People’s Republic of China

Keng H. Chung - Well Resources, Inc., Edmonton, Alberta, Canada

Suoqi Zhao - State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102200, People’s Republic of China

Yahe Zhang - State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102200, People’s Republic of China

Corresponding Author: Email xcm@cup.edu.cn

DOI: 10.1021/ef901564e

Keywords: Aromatic compounds;Hydrocarbons;Nitrogen;Organic polymers;Petrochemicals

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 N₁, N₂, N₁O₁, N₁O₂, N₁O₃, N₁O₄, O₁, and O₂ heteroatom classes. No molecules in the saturate fraction can be ionized by ESI. The aromatic fraction contains N₁ and N₁O_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 N₁, N₁O₁, and O₁ 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 N₁ and N₁O₁ class species. Neutral nitrogen compounds with molecular weights lower than 200 were discriminated in the FT-ICRMS 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 ofthe neutral nitrogen species were entrained in asphaltenes during the deasphalting step of sample fractionation.