5 Oil Pollution
5.1 The Composition of Petroleum
Petroleum has been formed from the organic remains of dead organisms over different
periods in the Earth's history. These organics have been preserved till the present in
fossil form in places where the absence of oxygen has prevented their decomposition.
Because different factors figured in the formation and settling of the different sediments, the quality of petroleum is different everywhere it is found. Thousands of
different compounds may be present in petroleum. 200-300 compounds are present
in any particular grade of crude oil. More than half, 500/0-98%, of petroleum consists of hydrocarbons, Le., compounds that contain carbon and hydrogen alone. The
following components can be identified in hydrocarbons (Fig. 41):
a) Alkanes (paraffines), which are related to methane, ethane, etc. that are also
present in oil deposits. Compounds with 5-7 carbon atoms are liquid; those with a
higher number of atoms are in a solid state. There are paraffms with over 60 carbon
atoms. Besides straight alkanes, there are branched isoalkanes. Alkanes are relatively
nonpoisonous and are biodegraded by many types of microbes. However, the more
ISOALKANES
c-c;:-c-C
C
ISOBUTANE
CYCLOALKANES
CJ
c
c-c-c-c-c I I
C C
ISOOCTANE
o
CYCLOPENTANE CYCLOHEXANE
c c c C
c-c- C3-C-C3-C-C3-C - C
PRISTANE (ISOPRENOiD)
00
TRI. TETRA AND PENTACYCLIC NAPHTHENES
AROMATICS
o co
BENZENE
NAPTHALENE
ANTHRACENE
PYRENE
Fig. 41. Structure of some petroleum
hydrocarbons
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