Origin of polar organic sulfur compounds in immature crude oils revealed by ESI FT-ICR MS

Weimin Liu^a,b, Yuhong Liao^a,*, Quan Shi^c, Chang Samuel Hsu^c,d,e, Bin Jiang^a, Ping’an Peng^a

^aState Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou 510640, PR China

^bUniversity of Chinese Academy of Sciences, Yuquan Road, Beijing 100049, PR China

^cState Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, PR China

^dPetro Oil Consulting, Tallahassee, FL 32312, USA

^eDepartment of Chemical and Biomedical Engineering, Florida A&M University/Florida State University, Tallahassee, FL 32310, USA

*Corresponding Authors: Yuhong Liao − Email: liaoyh@gig.ac.cn

DOI: 10.1016/j.orggeochem.2018.07.005

Keywords: Polar organic sulfur compounds; Sulfurization; ESI FT-ICR MS; Carotenoids

Abstract: Organic sulfur compounds (OSCs) are abundant in immature crude oils, including “polar” OSCs that are defined here as compounds containing one or more heteroatom(s) in addition to sulfur atoms having sufficient polarity to be analyzable by electrospray ionization (ESI) without derivatization. An understanding of the origins of polar OSCs in crude oils has been hampered by limitations in their analytical characterization. In this paper, we employed a high field (9.4 T) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with ESI to study the sulfur-rich immature crude oils from the Jianghan Basin in China. The results show that the polar OSCs usually have non-sulfur counterparts, i.e., heteroatom-containing compounds without sulfur, with similar carbon number ranges, but slightly lower DBE (double bond equivalence) distributions. The similar or even identical carbon number distributions of the polar OSCs and their non-sulfur counterparts indicate their inheritance from the same precursors. The sulfur rings in polar OSCs are formed by intramolecular sulfurization that leads to the increases in DBEs compared to their non-sulfur counterparts. The results also indicate that the number of sulfur rings that can be formed in polar OSCs is largely controlled by the number of available reactive functional groups in their precursors. This paper extends our knowledge of intramolecular sulfurization during early diagenesis, especially for polar heteroatom-containing compounds.