Distribution of Acids and Neutral Nitrogen Compounds in a Chinese Crude Oil and Its Fractions: Characterized by Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Quan Shi,^*,† Suoqi Zhao,^*,† Zhiming Xu,^† Keng H. Chung,^‡ Yahe Zhang,^† and Chunming Xu^†

^†State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, People’s Republic of China, and^‡Well Resources, Incorporated, 3919-149A Street, Edmonton, Alberta T6R 1J8, Canada

Corresponding Authors: Quan Shi - State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, People’s Republic of China;  Email: sq@cup.edu.cn sqzhao@cup.edu.cn

Suoqi Zhao - State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, People’s Republic of China;  Email: sq@cup.edu.cn sqzhao@cup.edu.cn

DOI: 10.1021/ef1004557

Keywords: Aromatic compounds; Ionization; Lipids; Petrochemicals; Transition temperature

Abstract: A Chinese crude oil was distilled into multiple narrow boiling fractions. The crude oil, 39 narrow distillate fractions (up to 560 °C), and atmospheric and vacuum residues were analyzed using negative electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The heteroatoms, N₁, N2, N1O1, N1O2, O1, and O2 class species, were identified and characterized by double-bond equivalent (DBE) values and carbon numbers. The composition of crude oil was correlated with increased boiling point. Most abundant O1 and O2 class species had DBE values and carbon numbers corresponding to biological skeleton structures, such as hopanoic acid, secohopanoic acid, and sterol. The distribution of acids and neutral nitrogen compounds in the various fractions were determined. At higher carbon numbers, the amount of the compounds and DBE values increased gradually with the boiling point for most oil fractions. The abundant N1 class species were centered at DBE values of 9, 12, 15, and 18. These were likely pyrrolic compounds with various numbers of aromatic rings. Species such as hopanoic acids and secohopanoic acids were highly abundant in fractions above 500 °C. Sterol-like compounds were enriched in the 460−500 °C fractions. These are likely the major species causing a high total acid number (TAN) in the crude oil.