information:extraction
Chemical analysis and production

Commercial gas is a mixture of a large number of different hydrocarbons. Chemical Gasoline is produced to meet a number of engine performance specifications and many different compositions are possible. Hence, the exact chemical composition of gasoline is undefined. The performance specification also varies with season, requiring less volatile blends during summer, in order to minimize evaporative losses. At the refinery, the composition varies according to the crude oils from which it is produced, the type of processing units present at the refinery, how those units are operated, and which hydrocarbon streams (blendstocks) the refinery opts to use when blending the final product.

Gasoline is produced in oil refineries. Roughly 72 liters (19 U.S. gal) of gasoline is derived from a 160-liter (42 U.S. gal) barrel of crude oil. Material separated from crude oil via distillation, called virgin or straight-run gasoline, does not meet specifications for modern engines (particularly the octane rating; see below), but can be pooled to the gasoline blend.

The bulk of a typical gasoline consists of a homogeneous mixture of small, relatively lightweight hydrocarbons with between 4 and 12 carbon atoms per molecule (commonly referred to as C4–C12). It is a mixture of paraffins (alkanes), olefins (alkenes), and napthenes (cycloalkanes). The use of the term paraffin in place of the standard chemical nomenclature alkane is particular to the oil industry. The actual ratio of molecules in any gasoline depends upon:

The various refinery streams blended to make gasoline have different characteristics. Some important streams include the following:

The terms above are the jargon used in the oil industry, and the terminology varies.

Currently, many countries set limits on gasoline aromatics in general, benzene in particular, and olefin (alkene) content. Such regulations have led to an increasing preference for alkane isomers, such as isomerate or alkylate, as their octane rating is higher than n-alkanes. In the European Union, the benzene limit is set at one percent by volume for all grades of automotive gasoline. This is usually achieved by avoiding feeding C6, in particular cyclohexane, to the reformer unit, where it would be converted to benzene. Therefore, only (desulfurized) heavy virgin naphtha (HVN) is fed to the reformer unit

Gasoline can also contain other organic compounds, such as organic ethers (deliberately added), plus small levels of contaminants, in particular organosulfur compounds (which are usually removed at the refinery).