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What is gasoline? Properties, composition and origin

What is gasoline? Properties, composition and origin

Gasoline is a mixture of hydrocarbons derived from petroleum that is used as fuel in internal combustion engines. It has a very high calorific value, about 46 MJ / kg.

Gasoline is a highly flammable, colorless liquid, not as dense as water (relative density: 0.70 to 0.75). Gasoline is obtained from oil by direct distillation, between 60° and 200°C, or by cracking the heavy fractions.

From a chemical point of view, gasoline is a mixture of alkanes, cycloalkanes, and aromatic compounds with 4 to 10 carbon atoms, and sometimes alkenes. Gasoline is mainly used as fuel in internal combustion engines. For this reason, this fuel must have a high anti-knock power, which is measured by the octane number (octane).

This antiknock power can be improved by changing the chemical composition, by refining procedures (cracking, reforming, isomerization, etc.) and by adding antiknock agents (tetraethyl lead). It is also used as a solvent in many applications, and the desired volatility is obtained by varying the end point of distillation.

What is gasoline made of?

It can be considered composed of a mixture of octane and nona hydrocarbons. Naphtha is normally considered to be the fraction of oil whose boiling point is approximately between 28 and 175 °C (threshold that varies depending on the commercial needs of the refinery). At the same time, this by-product is subdivided into light naphtha (up to about 100 °C) and heavy naphtha (the rest).

Light naphtha is one of the components of gasoline, with octane numbers around 70. Heavy naphtha does not have sufficient quality to be used for this purpose, and its destination is transformation through catalytic reforming, a chemical process by which hydrogen is also obtained, while increasing the octane number of this naphtha.

In addition to reformed naphtha and light naphtha, other components used in the formulation of a commercial gasoline are FCC naphtha, isomerized light naphtha, debenzenized pyrolysis gasoline, butane, butenes, MTBE, ETBE, alkylated and ethanol. . The formulas of each refinery are usually different (even belonging to the same companies), depending on the process units they have and depending on whether it is summer or winter.

Naphtha is obtained by a process called fluid catalytic cracking FCC (sometimes called FCC gasoline) from heavy diesel. If it is not refined, it can have up to 1000 ppm of sulfur. It has about 40% aromatics and 20% olefins. Its octane numbers (MON / RON) are around 80/93.

Isomerized light naphtha (isomers) is obtained from light naphtha by direct distillation, through a process that uses solid catalysts based on platinum/aluminum or zeolites. It is a component free of sulfur, benzene, aromatics and olefins, with octane numbers (MON / RON) around 87/89.

Debenzenized pyrolysis gasoline obtained as a by-product of the manufacture of ethylene from light naphtha. It is composed of approximately 50% aromatics (toluene and xylenes) and 50% olefins (isobutene, hexene). It has about 200 ppm sulfur. The benzene it contains at source is usually purified and sold as a petrochemical raw material. Its octane numbers (MON / RON) are around 85/105

The alkylate is obtained from isobutane and butenes, through a process that uses acid catalysts (either sulfuric acid or hydrofluoric acid). It also has no sulfur, benzene, aromatics or olefins. Its octane numbers (MON / RON) are around 94/95.

Where is gasoline extracted from?

Oil Refinery - Gasoline ManufacturingGasoline is a derivative of crude oil and is obtained in a refinery. In general, it is obtained from direct distillation naphtha, which is the lightest liquid fraction of petroleum (except gases).

Naphtha is also obtained from the conversion of heavy oil fractions (vacuum gas oil) in process units called FCC (fluidized catalytic cracking) or hydrocracatge.

A series of specifications required for the engine to work well and other environmental specifications must be met, both regulated by law in most countries. The most characteristic specification is the octane number, which indicates its tendency to detonate.

There are different types of commercial gasoline, classified according to their octane number. The best-selling gasoline in Europe (2004) has a minimum MON of 85 and a minimum RON of 95.

Generation of carbon dioxide from gasoline

Approximately 2.36kg of carbon dioxide (CO 2 ) are generated by burning 1 liter of gasoline that does not contain ethanol. From 1 liter of diesel fuel, 2.69 kg of CO2 are generated.

The US EIA estimates that US gasoline (distillate) and motor fuel consumption for transportation in 2015 resulted in the emission of approximately 1,105 million metric tons of CO2  and  440 million metric tons of carbon dioxide, respectively, for a total of 1,545 million metric tons of CO 2  . This total was equivalent to 83% of total US transportation sector carbon dioxide emissions and equivalent to 29% of total US energy-related carbon dioxide emissions in 2015 .

Most of the retail gasoline now sold in the United States contains about 10% fuel ethanol (or E10) by volume. Burning one gallon of E10 produces approximately 17.68 pounds (8.02 kg) of carbon dioxide that is emitted from fossil fuel content.

If carbon dioxide emissions from ethanol combustion are considered, about 18.95 pounds (8.60 kg) of carbon dioxide are produced when one gallon of E10 is burned. About 12.73 pounds (5.77 kg) of carbon dioxide are produced when one gallon of pure ethanol is burned.

Publication Date: November 17, 2016
Last Revision: February 26, 2019