176 7 Pollution of Aquatic Systems: Pollution Through Eutrophication, Fecal Materials, and Oil Spills
polar compounds. Their elements contain, in addition
to carbon and hydrogen, trace amounts of nitrogen,
sulfur, and/or oxygen. These compounds often form
complexes with heavy metals.
Asphaltenes consist of high-molecular-weight com-
pounds, which are not soluble in a solvent such as n-hep-
tane, while resins are n-heptane-soluble polar molecules.
Resins contain heterocyclic compounds, acids, and
sulfoxides. The components of petroleum in crude oil
have been analyzed mainly by using gas chromatogra-
phy in combination with mass spectrometry (GC/MS).
Consequently, the chemical structures of the higher-
molecular-weight components (the heavy fractions)
that cannot be identified by GC are mostly unknown.
Furthermore, the compositions of many branched
alkanes and alkyl cycloalkanes have not been deter-
mined because their isomers are numerous and cannot
be resolved by gas chromatography. Many compounds
in crude oil are yet to be identified.
During refining, many products are obtained from
crude oil by fractional distillation, yielding different
fractions or cuts. Alkenes, unsaturated hydrocarbons
including ethylene, are not found in crude oil, but are
Fig. 7.6 Various hydrocarbons (From Harayama et al. 1999 ) produced during the refining or cracking of crude oil.
Table 7.8 Gross compositions of crude oils from different
parts of the world (From http://www.petroleumhpv.org/docs/
crude_oil/111503_crude_robsumm_final.pdf. Reproduced cour-
tesy of the American Petroleum Institute from Robust Summary
of Information on Crude Oil, 2003; Anonymous 2003 )Country or origin of crude
Paraffin Naphthalenes Aromatics Sulfur API gravity
vol% vol% vol% wt% (°API)
Light crudes
Saudi Light 63 18 19 20 34
South Louisiana 79 45 19 0 35
Nigerian Light 37 54 9 0.1 36
North Sea Brent 50 34 16 0.4 37
Beryl 47 34 19 0.4 32
Lost Hill Nonaromatics 50 50 0.9
Mid-range crudes
Kuwait 63 26 24 24 31
Venezuela Light 52 34 14 1.5 30
USA West Texas Sour 46 32 22 1.9 32
Heavy crudes
Prudhoe Bay 27 36 15 2.1 28
Saudi Heavy 60 20 15 2.1 28
Venezuela Heavy 35 53 12 23 24
Belridge Heavy Nonaromatics 37 63 1.1 –