Petroleum Composition
By Anne Marie Helmenstine, Ph.D.
Petroleum or crude oil is any naturally-occurring flammable mixture of hydrocarbons found in geologic formations, such as rock strata. Most petroleum is a fossil fuel, formed from the action of intense pressure and heat on buried dead zooplankton and algae. Technically, the term petroleum only refers to crude oil, but sometimes it is applied to describe any solid, liquid or gaseous hydrocarbons. Petroleum or crude oil is a complex mixture of hydrocarbons and other chemicals. The composition varies widely depending on where and how the petroleum was formed. In fact, chemical analysis can be used to fingerprint the source of petroleum. However, raw petroleum or crude oil has characteristic properties and composition.
Composition of Petroleum
Petroleum consists primarily of paraffins and naphthenes, with a smaller amount of aromatics and asphaltics. Near the surface, lighter hydrocarbons (methane, ethane, propane, butane) are gases. Heavier compounds are liquids or solids. Trace metals include iron, copper, nickel, and vanadium. The chemical composition of a specimen is a sort of fingerprint for the source of the petroleum.
The chemical composition also determines the color of petroleum. Often, it is black or brown, but it may be reddish, yellow, or green.
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.
SOURCE: https://www.thoughtco.com/chemical-composition-of-petroleum-607575
