or crude oil is a complex mixture of hydrocarbons and other chemicals. The composition varies widely depending where and how the petroleum was formed. In fact, a chemical analysis can be used to fingerprint the source of the petroleum. However, raw petroleum or crude oil has characteristic properties and composition.
Hydrocarbons in Crude Oil
There are four main types of hydrocarbons found in crude oil.
- paraffins (15-60%)
- naphthenes (30-60%)
- aromatics (3-30%)
- asphaltics (remainder)
The hydrocarbons primarily are alkanes, cycloalkanes and aromatic hydrocarbons.
Elemental Composition of Petroleum
Although there is considerable variation between the ratios of organic molecules, the elemental composition of petroleum is well-defined:
- Carbon - 83 to 87%
- Hydrogen - 10 to 14%
- Nitrogen - 0.1 to 2%
- Oxygen - 0.05 to 1.5%
- Sulfur - 0.05 to 6.0%
- Metals - < 0.1%
The most common metals are iron, nickel, copper and vanadium.
Petroleum Color and Viscosity
The color and viscosity of petroleum vary markedly from one place to another. Most petroleum is dark brown or blackish in color, but it also occurs in green, red or yellow.