Why Are Hydrocarbons Important in Crude Oil?

From powering cars to manufacturing pharmaceuticals, crude oil is used for a myriad of applications. The complex molecular resource is made up largely of comparatively volatile liquid hydrocarbons, which are essentially compounds of hydrogen and carbon. Crude oil also contains traces of nitrogen, sulphur and oxygen, though hydrogen and carbon are the main components.

By weight, most crude oil contains around 82 to 87% carbon and 12 to 15% hydrogen. Classification of crude oils depends largely on the type of hydrocarbon compound that's most dominant, either paraffins, naphthenes or aromatics. For this reason, the hydrocarbon content of crude oil is extremely important.

Paraffins, naphthenes and aromatics

Paraffins are the most common hydrocarbons found in crude oil, with the constituents made up of molecules containing between twenty and forty carbon atoms. Certain types of liquid paraffins allow crude to be processed into gasoline, which makes paraffin-rich crude oil highly valuable.

Naphthenes, including cyclohexane and cyclopropane, are a group of cyclic aliphatic hydrocarbons used to create liquid refinery products. Aromatics account for a small percentage of extracted crude oil, with the most common organic chemical compound being benzene. Others include toluene and xylenes, which are used as starting materials for manufacturing petrochemical products.

Significant variations in hydrocarbon content mean the physical properties of crude oil, as well as the applications the resource is used for, vary greatly. For example, depending on hydrocarbon makeup crude oil can range from clear and colourless to viscous and black.

Sweet or sour

Depending on the level of sulphur, a chemical element that occurs either as an elemental property or in the form of compounds, crude oil is categorised as sweet or sour. By weight, sweet crudes feature sulphur contents of 0.5 percent or less, while sour crudes are made up of at least 1% or higher. In general, heavier crudes have higher sulphur content.

During the refining process, excess sulphur is removed from crude oil as the chemical element releases harmful oxides during combustion that pollute the atmosphere. The sulphur content of crude, which is determined by hydrocarbon properties, will determine what type of refinery the oil is sent to.

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