Insight into unresolved complex mixtures of aromatic hydrocarbons in heavy oil via two-dimensional gas chromatography coupled with time-of-flight mass spectrometry analysis.
The aromatic hydrocarbon fractions of five crude oils representing a natural sequence of increasing degree of biodegradation from the Liaohe Basin, NE, China, were analyzed using conventional gas chromatography-mass spectrometry (GC-MS) and comprehensive two-dimensional gas chromatography (GC×GC). Because of the limited peak capability and low resolution, compounds in the aromatic fraction of a heavily biodegraded crude oil that were analyzed by GC-MS appeared as unresolved complex mixtures (UCMs) or GC "humps". They could be separated based on their polarity by GC×GC. UCMs are composed mainly of aromatic biomarkers and aromatic hydrocarbons with branched alkanes or cycloalkanes substituents. The quantitative results achieved by GC×GC-FID were shown that monoaromatic hydrocarbons account for the largest number and mass of UCMs in the aromatic hydrocarbon fraction of heavily biodegraded crude oil, at 45% by mass. The number and mass of diaromatic hydrocarbons ranks second at 33% by mass, followed by the aromatic biomarker compounds, triaromatic, tetraaromatic, and pentaaromatic hydrocarbons, that account for 10%, 6%, 1.5%, and 0.01% of all aromatic compounds by mass, respectively. In the heavily biodegraded oil, compounds with monocyclic cycloalkane substituents account for the largest proportion of mono- and diaromatic hydrocarbons, respectively. The C4-substituted compounds account for the largest proportion of naphthalenes and the C3-substituted compounds account for the largest proportion of phenanthrenes, which is very different from non-biodegraded, slightly biodegraded, and moderately biodegraded crude oil. It is inferred that compounds of monoaromatic, diaromatic and triaromatic hydrocarbons are affected by biodegradation, that compounds with C1-, C2-substituents are affected by the increase in degree of biodegradation, and that their relative content decreased, whereas compounds with C3-substituents or more were affected slightly or unaffected, and their relative content also increased. The varying regularity of relative content of substituted compounds may be used to reflect the degree of degradation of heavy oil. Moreover, biomarkers for the aromatic hydrocarbons of heavily biodegraded crude oil are mainly aromatic steranes, aromatic secohopanes, aromatic pentacyclotriterpanes, and benzohopanes. According to resultant data, aromatic secohopanes could be used as a specific marker because of their relatively high concentration. This aromatic compound analysis of a series of biodegraded crude oil is useful for future research on the quantitative characterization of the degree of biodegradation of heavy oil, unconventional oil maturity evaluation, oil source correlation, depositional environment, and any other geochemical problems.
Research Institute of Petroleum Exploration and Development, PetroChina, 20 Xueyuan Road, Haidian District, Beijing 100083, China.
Na
N
Weng
Department of Environment Engineering and Chemistry, Luoyang Institute of Science and Technology, 90, Wangcheng Road, Luoyang 471023, Henan, China.
Shan
S
Wan
Research Institute of Petroleum Exploration and Development, PetroChina, 20 Xueyuan Road, Haidian District, Beijing 100083, China.
Huitong
H
Wang
Research Institute of Petroleum Exploration and Development, PetroChina, 20 Xueyuan Road, Haidian District, Beijing 100083, China.
Shuichang
S
Zhang
Research Institute of Petroleum Exploration and Development, PetroChina, 20 Xueyuan Road, Haidian District, Beijing 100083, China.
Guangyou
G
Zhu
State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, China.
Jingfu
J
Liu
Research Institute of Petroleum Exploration and Development, PetroChina, 20 Xueyuan Road, Haidian District, Beijing 100083, China.
Di
D
Cai
Department of Chemistry and Chemical Engineering, School of Chemistry and Biological Engineering, University of Science and Technology, 30 Xueyuan Road, Haidian District, Beijing 100083, China. Electronic address: yxyang@ustb.edu.cn.
Yunxu
Y
Yang
D000473:Alkanes / Q000032:analysis; D001673:Biodegradation, Environmental; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D002681:China; D008401:Gas Chromatography-Mass Spectrometry; D006841:Hydrocarbons, Aromatic / Q000032:analysis*; D009281:Naphthalenes / Q000032:analysis; D010578:Petroleum / Q000032:analysis*; D010616:Phenanthrenes / Q000032:analysis
D000473:Alkanes; D006841:Hydrocarbons, Aromatic; D009281:Naphthalenes; D010578:Petroleum; D010616:Phenanthrenes
Biodegraded crude oil; Comprehensive two-dimensional chromatography; Heavy oil; Time-of-flight mass spectrometry; UCM