page_title: Gasoline
section_title: Chemical analysis and production
hierarchical_section_title: Gasoline / Chemical analysis and production
caption_attribution_description: Offshore platform located in the Gulf of Mexico, port location Cd. Del Carmen.
context_page_description: Gasoline, or petrol is a clear petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. On average, a 160-liter barrel of crude oil can yield up to about 72 liters of gasoline after processing in an oil refinery, depending on the crude oil assay and on what other refined products are also extracted.
  The characteristic of a particular gasoline blend to resist igniting too early is measured by its octane rating, which is produced in several grades. Once widely used to increase octane rating, tetraethyl lead and other lead compounds are no longer used in most areas. Other chemicals are frequently added to gasoline to improve chemical stability and performance characteristics, control corrosiveness and provide fuel system cleaning. Gasoline may contain oxygen-containing chemicals such as ethanol, MTBE or ETBE to improve combustion.
  Gasoline can enter the environment uncombusted, both as liquid and as vapor, from leakage and handling during production, transport and delivery.
context_section_description: Commercial gasoline is a mixture of a large number of different hydrocarbons.  Gasoline is produced to meet a host 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, with more volatile blends (due to added butane) during winter, in order to be able to start a cold engine.  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 19 U.S. gallons (72 L) of gasoline is derived from a 42-U.S.-gallon (160 L) 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 cycloalkanes (naphthenes). The usage of the terms paraffin and olefin in place of the standard chemical nomenclature alkane and alkene, respectively, is particular to the oil industry. The actual ratio of molecules in any gasoline depends upon:
  the oil refinery that makes the gasoline, as not all refineries have the same set of processing units;
  the crude oil feed used by the refinery;
  the grade of gasoline (in particular, the octane rating).
  The various refinery streams blended to make gasoline have different characteristics. Some important streams include:
  straight-run gasoline, commonly referred to as naphtha, which is distilled directly from crude oil. Once the leading source of fuel, its low octane rating required lead additives. It is low in aromatics (depending on the grade of the crude oil stream) and contains some cycloalkanes (naphthenes) and no olefins (alkenes). Between 0 and 20 percent of this stream is pooled into the finished gasoline, because the quantity of this fraction in the crude is less than fuel demand and the fraction's RON is too low. The chemical properties (namely RON and Reid vapor pressure) of the straight-run gasoline can be improved through reforming and isomerisation. However, before feeding those units, the naphtha needs to be split into light and heavy naphtha. Straight-run gasoline can also be used as a feedstock for steam-crackers to produce olefins.
  reformate, produced in a catalytic reformer, has a high octane rating with high aromatic content and relatively low olefin content. Most of the benzene, toluene and xylene (the so-called BTX hydrocarbons) are more valuable as chemical feedstocks and are thus removed to some extent.
  catalytic cracked gasoline, or catalytic cracked naphtha, produced with a catalytic cracker, has a moderate octane rating, high olefin content and moderate aromatic content.
  hydrocrackate (heavy, mid and light), produced with a hydrocracker, has a medium to low octane rating and moderate aromatic levels.
  alkylate is produced in an alkylation unit, using isobutane and olefins as feedstocks. Finished alkylate contains no aromatics or olefins and has a high MON.
  isomerate is obtained by isomerizing low-octane straight-run gasoline into iso-paraffins (non-chain alkanes, such as isooctane). Isomerate has a medium RON and MON, but no aromatics or olefins.
  butane is usually blended in the gasoline pool, although the quantity of this stream is limited by the RVP specification.
  The terms above are the jargon used in the oil industry and 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 isomera
caption: An oil rig in the Gulf of Mexico
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