Variations of acidic compounds in crude oil during simulated aerobic biodegradation: Monitored by semiquantitative negative-ion ESI FT-ICR MS

Yinhua Pan, Yuhong Liao*and Quan Shi

The State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 511 Kehua Street, Wushan Road, Tianhe District, Guangzhou, GD 510640, China

*University of Chinese Academy of Sciences, Yuquan Road, Beijing 100049, China

Sinopec Key Laboratory of Petroleum Accumulation Mechanisms, Wuxi Research Institute of Petroleum Geology, Sinopec Petroleum Exploration & Production Research Institute, 2060 Lihu Road, Binhu District, Wuxi, Jiangsu 214000, China

State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China

Corresponding Author: *Telephone: +86-20-8529-1567. Fax: +86-20-8529-0706. E mail: liaoyh@gig.ac.cn.

DOI: 10.1021/acs.energyfuels.6b02167

Keywords: Biodegradation; Chromatography; Hydrocarbons; Lipids; Petrochemicals

Abstract: Simulations of aerobic biodegradation have been widely employed to investigate the mechanisms of crude oil biodegradation in geological environments. In this study, a simulated biodegradation experiment was performed with crude oil under aerobic conditions, in which n-alkanes were nearly depleted, thus providing an opportunity to study the biodegradation mechanisms of nalkanes in crude oils. The sequences of biodegraded oils with a slight to moderate degree of biodegradation were characterized by negative-ion electrospray (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and gas chromatography (GC). Semiquantitative results on the molecular compositions of heteroatom classes were obtained by coinjection of internal standards. The biodegradation mechanisms for n-alkanes and n-fatty acids, as well as some other heteroatomic compounds, are discussed. Evidence from FT-ICR MS and GC analyses of biodegraded oils indicates that nalkanes can be progressively biodegraded to n-fatty acids through β-oxidation, or to hydroxycarboxylic and dicarboxylic acids though ω-oxidation. The O₃ class species which have a high relative abundance in the carbon number range of C₃₃−C₃₈ with a Double Bond Equivalent (DBE) of 1−3 were assigned and speculated to be bacterial metabolites, which could be a conspicuous indicator of bacterial activity. Neutral nitrogen compounds, such as carbazoles, exhibited a very slight decrease in the stage of biodegradation that was investigated.