Supplementary data
The ratios of vanadium-to-nickel and phenanthrene-to-dibenzothiophene as means of
identifying petroleum source and classification of Nigeria crude oils
A.S. Ogunlaja,1,* O.S. Alade,2 E.O. Odebunmi,3 A. Majavu,4 N. Torto1 and Z.R. Tshentu1,4
1
Department of Chemistry, Rhodes University, P.O. Box 94, Grahamstown 6139, South
Africa.
2
Petroleum and Petrochemical Engineering Laboratory, Department of Chemical
Engineering, Obafemi Awolowo University, P.O. Box 004, Ife, Osun State, Nigeria.
3
Department of Chemistry, University of Ilorin, PMB 1515, Ilorin, Kwara state, Nigeria.
4
Department of Chemistry, Nelson Mandela Metropolitan University, P.O. Box 77000, Port
Elizabeth, 6031, South Africa.
1.
Column separation protocol of the Crude oils
A 0.5 g of crude oil sample was dissolved in 10 mL of pentane and allowed to stand for 4 h,
then centrifuged at 10,000 rpm for 30 mins to separate the pentane soluble from the
asphaltenes. The fractionation was carried out in column (about 2-3 cm diameter) packed
with 14 g of silica gel. For this purpose, the column will be pre-wet with 5 mL hexane.
Elution was carried out by using 25 mL of n-hexane for saturates, 25 mL of dichloromethane
for aromatics and 25 mL mixture of dichloromethane: methanol (1:1) was used to elute the
resins. Drying of the various fractions was done in the fume hood by bubbling nitrogen gas in
the samples in vials. The fractionated products were analyzed by using FT-IR and GC-MS.
2.
FT- IR spectroscopy
A broad band around 3330-3420 cm-1 was assigned to ν(O-H) and ν(R-NH-R) group, this
bands were observed in the medium and heavy crude oils with heavy crude oil far broader
than that of the medium crude oil. The high intensity of the bands signifies the presence of
more bonded hydroxyl and amino containing compounds. Most important set of bands for the
aromatic ring vibrations is centered in the region 1650-1550 cm-1, this usually occur as a pair
of band structures, often with some splitting. C-H aromatic stretch of methyl groups was
observed around 2960 and 2920 cm-1, respectively exhibiting a multiplicity of weak-tomoderate bands. Thiols (C-S) and (C-S-H) stretching vibrations occurred between the
vibrational frequencies of 720–800 cm-1 on all the crude oil aromatic fractions.
A
% Transmittance
% Transmittance
B
Light crude oil (aromatics)
Medium crude oil (aromatics)
Light crude oil (saturates)
Heavy crude oil (aromatics)
Heavy crude oil (saturates)
Medium crude oil (saturates)
4000
3000
2000
1000
Wavelenght (cm-1)
Figure S1.
4000
3000
2000
1000
Wavelenght (cm-1)
FT-IR spectra for the aromatic (a) and saturate (b) fractions of the Light,
Medium, and Heavy crude oils
3.
GC-MS
3.1
GC-MS method
Hewlett Packard 6890 series gas chromatograph (GC), fitted with a mass spectrometer (MS) and an
agilent-5MSi capillary column (30m×0.25mm×0.25µm) was used for analysis of the organics. The
GC oven was started at 50°C, held isothermally for 2.0 min, and then programmed to 300°C at
5°C/min. while MS ion source temperature of 250°C with a scan range of m/z 60 to 500 was
employed.
3.2
GC-MS data
GC-MS analyses of the oils (light, medium and heavy) are presented below.
Light crude oils
A
B
C
Figure S2.
GCMS analysis of (A) Light crude oil (aromatic fraction), (B) phenanthrenes
with derivatives, (C) dibenzothiophene with derivatives.
Medium crude oil
A
B
C
Figure S3.
GCMS analysis of (A) Medium crude oil (aromatic fraction), (B)
phenanthrenes with derivatives, (C) dibenzothiophene with derivatives.
Heavy Crude oil
A
B
C
Figure S4.
GCMS analysis of (A) Heavy crude oil (aromatic fraction), (B) phenanthrenes
with derivatives, (C) dibenzothiophene with derivatives.
10
V/Ni
P:D
Ratios (V/Ni and P:D)
8
6
4
2
0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Sulfur (wt %)
Figure S5.
Graph showing the relationship between V/Ni and P/D to sulfur content of oil
(wt%).