AROMATIC HYDROCARBONS AND INFRARED SPECTROSCOPIC CHARACTERISATION OF NORTHWESTERN NIGER DELTA OILS
A. Akinlua 1*, N. Torto2 and T. R. Ajayi3
1 Department of Chemistry, Obafemi Awolowo University, Ile-Ife, Nigeria.
2 Department of Chemistry, University of Botswana, P/Bag UB 00704, Gaborone, Botswana.
3 Department of Geology, Obafemi Awolowo University, Ile-Ife, Nigeria.
* Corresponding author, email: stevesanya@yahoo.com
Key words: Aromatic hydrocarbons, infrared spectroscopy, oil, Niger Delta, biodegradation, maturity
The occurrence and distribution of aromatic hydrocarbons in oils from the NW Niger Delta was investigated, focussing on naphthalenes, phenanthrenes monoaromatic and triaromatic steroids. Tetramethylnaphthalene is most abundant of the naphthalene homologues, while dimethylphnanthrene is the most abundant of the phenanthrene homologues. The relative concentration of the sum total of the phenanthrenes and their isomers was greater than that of the naphthalenes.
The distribution of naphthalenes and phenanthrenes was strongly controlled by thermal maturation and biodegradation of the oils. Various aromatic-hydrocarbon dependent geochemical parameters indicate that the oils are mature and were generated at almost the same level of thermal maturation. Different aromatic hydrocarbon-based geochemical plots showed that the distribution of some homologues of both naphthalene and phenanthrene is sensitive to the biodegradation of the oils.
Infrared spectroscopy was used for geochemical characterisation of the Niger Delta oils in terms of source and thermal maturity. The characterisation was based on the peak intensities of the aliphatic and the carbonyl groups relative to the aromatics. The study showed that IR may be useful for the determination of thermal maturity, but is not a good tool for source characterisation.
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