Gasoline is an easily flammable liquid, colorless, not as dense as water (relative density: 0.70 to 0.75). Gasoline is obtained from petroleum by direct distillation, between 60 ° and 200 ° C, or by cracking heavy fractions.
From a chemical point of view, gasoline is a mixture of alkanes, cycloalkanes and aromatic compounds of 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 (octane) index.
This antidetonating power can be improved by variation of the chemical composition, by refining procedures (cracking, reforming, isomerization, etc.) and by the addition of antidetonating agents (tetraethylplom). It is also used as a solvent in many applications, and the desired volatility is obtained by varying the end point of distillation.
It can be considered composed of a mixture of the octane and nona hydrucarburs. Normally, the fraction of oil whose boiling point is approximately between 28 and 175 ° C (threshold that varies according to the commercial needs of the refinery) is considered naphtha. At the same time, this by-product is subdivided into light gasoline (up to about 100 ° C) and heavy gasoline (the rest). Light gasoline is one of the components of gasoline, with octane rates around 70. Heavy gasoline is not of sufficient quality to be used for this purpose, and its destination is the transformation by catalytic reforming, chemical process by which also obtains hydrogen, while increasing the octane number of this gasoline.
In addition to the reformed gasoline and light gasoline, other components that are used in the formulation of a commercial gasoline are FCC gasoline, light isomerized gasoline, benzyl 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 available and depending on whether it is summer or winter.
Naphtha is obtained by a process called FCC cracking catalytic fluid (sometimes called FCC gasoline) of heavy diesel. If it is not refined it can have up to 1000 ppm of sulfur. It has about 40% aromatics and 20% olefins. Their octane indices (MON / RON) are around 80/93.
Isomeritized light naphtha (isomers) is obtained from light direct distillation naphtha, using a process using solid platinum / aluminum or zeolitic base catalysts. It is a free component of sulfur, benzene, aromatics and olefins, with octane levels (MON / RON) around 87/89.
Debenzenitized pyrolysis gasoline obtained as a byproduct 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 of sulfur. The benzene that it contains in origin is usually purified and sold as a petrochemical raw material. Its octane indices (MON / RON) are around 85/105
The alkylate is obtained from isobutane and butenes, by a process that uses acid catalysts (either sulfuric acid, or hydrofluoric acid). Nor does it have sulfur, benzene, aromatics or olefins. Its octane indices (MON / RON) are around 94/95.
Gasoline 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 fractions of oil (vacuum diesel) into process units called FCC (fluidized catalytic cracking) or hydrocracatge.
A series of specifications required for the engine to work well and others of an environmental type, both regulated by law in most countries, must be met. The most characteristic specification is the octane index, which indicates its tendency to detonate.
There are different types of commercial gasoline, classified according to their octane index. 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 generated carbon dioxide (CO2 ) to the burning 1 liter of gasoline containing no ethanol. 2.69 kg of CO2 are generated from 1 liter of diesel fuel.
The US EIA UU. Estimate that the consumption of engine fuel and gasoline (distillate) from the USA. UU. 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 CO2 . This total was equivalent to 83% of the total carbon dioxide emissions of the US transportation sector. UU. And equivalent to 29% of the total of carbon dioxide related to the energy of the EE. UU. In 2015.
Most of the retail gasoline that is now sold in the United States contains about 10% fuel ethanol (or E10) by volume. Burning a gallon of E10 produces approximately 17.68 pounds (8.02 kg) of carbon dioxide that is emitted from the fossil fuel content. If carbon dioxide emissions from ethanol combustion are considered, about 18.95 pounds (8.60 kg) of carbon dioxide is produced when a gallon of E10 is burned. About 12.73 pounds (5.77 kg) of CO2 are produced when a gallon of pure ethanol is burned.
The first automobile combustion engines, the so-called otto engines or gasoline engines, have been developed in the last quarter of the 19th century in Germany. The fuel was a relatively volatile hydrocarbon obtained from coal gas. With a boiling point near 85 ° C (boiling octane approximately 40 ° C higher), it was very suitable for the first carburetors (evaporators). The development of a carburetor "filter" allowed the use of less volatile fuels.
Other improvements in engine efficiency were attempted with high compression ratios, but the first attempts were blocked by detonations (premature fuel explosion). In the 1920s, antidetonating compounds were introduced by Thomas Midgley and Boyd, specifically tetraethylplom (TEL). This innovation began a cycle of improvements in fuel efficiency that coincided with the large-scale development of oil refining to provide more products in the boiling range of gasoline.
In the 1950s oil refineries began to focus on high octane fuels, and then gasoline detergents were added to clean the jets in the carburetors. The 1970s witnessed increased attention to the environmental consequences of gasoline combustion. These considerations led to the gradual elimination of TEL and its replacement by other antidetonating compounds. Subsequently, low sulfur gasoline was introduced, in part to preserve the catalysts in modern exhaust systems.