Gasoline

:Petrol (petroleum spirit) redirects here. For the seabird, see petrel, spelt with an 'e'.

Chemical analysis and production

Gasoline is produced in oil refineries. These days, material that is simply separated from crude oil via distillation, called natural gasoline, will not meet the required specifications (in particular octane rating; see below) for modern engines, but these streams will form part of the blend.

Related Topics:
Oil refineries - Crude oil - Distillation - Octane rating

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The bulk of a typical gasoline consists of hydrocarbons with between 5 and 12 carbon atoms per molecule.

Related Topics:
Hydrocarbon - Carbon - Atom - Molecule

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The various refinery streams that are blended together to make gasoline all have different characteristics. Some important streams are:

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• Reformate, produced in a catalytic reformer with a high octane and high aromatics content, and very low olefins (alkenes).
• Cat Cracked Gasoline or Cat Cracked Naphtha, produced from a catalytic cracker, with a moderate octane, high olefins (alkene) content, and moderate aromatics level. Here, "cat" is short for "catalyst".
• Hydrocrackate (Heavy, Mid, and Light), produced from a hydrocracker, with medium to low octane and moderate aromatic levels.
• Natural Gasoline (has very many names), directly from crude oil with low octane, low aromatics (depending on the crude oil), some naphthenes (cycloalkanes) and zero olefins (alkenes).
• Alkylate, produced in an alkylation unit, with a high octane and which is pure paraffin (alkane), mainly branched chains.
• Isomerate (various names) which is made by isomerising Natural Gasoline to increase its octane rating and is very low in aromatics and benzene content.

(The terms used here are not always the correct chemical terms. Typically they are old fashioned, but they are the terms normally used in the oil industry. The exact terminology for these streams varies by oil company and by country.)

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Overall a typical gasoline is predominantly a mixture of paraffins (alkanes), naphthenes (cycloalkanes), aromatics and olefins (alkenes). The exact ratios can depend on

Related Topics:
Alkanes - Cycloalkane - Aromatic - Alkene

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• the oil refinery that makes the gasoline, as not all refineries have the same set of processing units.
• the crude oil used by the refinery on a particular day.
• the grade of gasoline, in particular the octane.

These days, gasoline in many countries has tight limits on aromatics in general, benzene in particular, and olefins (alkene) content. This is increasing the demand for high octane pure paraffin (alkane) components, such as alkylate, and is forcing refineries to add processing units to reduce the benzene content.

Related Topics:
Aromatic - Benzene - Alkene - Alkane

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Gasoline can also contain some other organic compounds: such as organic ethers, (deliberately added) plus small levels of contaminants, in particular sulfur compounds such as disulfides and thiophenes. Some contaminants, in particular mercaptans and hydrogen sulfide must be removed because they cause corrosion in engines.

Related Topics:
Organic compound - Organic ether - Sulfur - Disulfides - Thiophene - Mercaptans - Hydrogen sulfide

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Volatility

Gasoline is more volatile than diesel or kerosene, not only because of the base constituents, but because of the additives that are put into it. The final control of volatility is often via blending of butane. The desired volatility depends on the ambient temperature: the hotter the weather, the lower the volatility. In Australia the volatility limit changes every month and differs for each main distribution center, but most countries simply have a summer, winter and perhaps intermediate limit.

Related Topics:
Diesel - Kerosene - Additive - Volatility - Butane - Australia

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The maximum volatility of gasoline in many countries has been reduced in recent years to reduce the fugitive emissions during refueling.

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Volatility standards may be relaxed (allowing more gasoline components into the atmosphere) during emergency anticipated gasoline shortages. For example, on 31 August 2005 in response to Hurricane Katrina, the United States activated an early switch to "winter gasoline" which has a volatility limit exceeding the usual summertime standard. As mandated by EPA administrator Stephen L. Johnson, this "fuel waiver" was made effective through 15 September 2005 http://www.epa.gov/katrina/activities.html#aug31johnson. Though relaxed volatility standards negatively impact ozone and other air quality criteria, higher volatility gasoline (which contains less additives than gasoline whose volatility has been artificially lowered) essentially increases a nation's gasoline supply.

Related Topics:
Hurricane Katrina - EPA - Stephen L. Johnson - Ozone

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Octane rating

The most important characteristic of gasoline is its octane rating, which is a measure of how resistant gasoline is to premature detonation (knocking). It is measured relative to a mixture of 2,2,4-trimethylpentane (an isomer of octane) and n-heptane. An 87-octane gasoline has the same knock resistance as a mixture of 87% isooctane and 13% n-heptane. The octane rating system was developed by the chemist Russell Marker.

Related Topics:
Octane rating - Knocking - 2,2,4-trimethylpentane - Isomer - Octane - Heptane - Knock resistance - Russell Marker

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