Petroleum hydrocarbons are naturally occurring organic compounds that are used by humans in a variety of ways. We use petroleum products, or petrochemicals to fuel cars, heat homes and make many types of plastics. Crude oil, tar, natural gas, and asphalt are all petroleum hydrocarbons which are composed of various proportions of hydrocarbon compounds. Classes of these compounds include alkanes, aromatics, and polycyclic aromatic hydrocarbons (PAHs). Non-hydrocarbon components and small amounts of metals are often also present in total petroleum hydrocarbons or TPH.
Alkanes:
This class of hydrocarbon is composed
of branched or non-branched chains of carbon (C) and hydrogen (H). They
vary in length, or number of carbons present in each molecule.
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Aromatics:
This class of hydrocarbon consist of cyclical
carbon (C) and hydrogen (H). This is known as a benzene ring and consists
of 6 carbons bound together in a ring with three double bonds and one hydrogen
atom per carbon. Different compounds result when a functional group
is substituted for a hydrogen.
Benzene ring Toluene Ethylbenzene
Benzene, toluene, ethylbenzene, and xylene (a ring with two methyl groups) are collectively known as BTEX compounds; which are important constituents of gasoline.
Polycyclic aromatic hydrocarbons (PAHs):
The fusion of two or more benzene rings
results in PAHs. These compounds are found virtually everywhere in the
environment in small concentrations. They are generally formed when fuel
is burned.