Gasoline

 

Gasoline is a transparent, petroleum-derived liquid that is used primarily as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasoline stations provide an ethanol additive as an alternative fuel.

Roughly 19 gallons of gasoline is derived from a 42 gallon barrel of crude oil. Material separated from crude oil via distillation, called virgin or straight-run gasoline, does not meet specifications for modern engines.

Typical gasoline consists of hydrocarbons with between 4 and 12 carbon atoms per molecule (commonly referred to as C4-C12). The various refinery streams blended to make gasoline have different characteristics, predominantly a mixture of paraffins (alkanes), cycloalkanes (naphthenes), and olefins (alkenes).

Currently, many countries set limits on gasoline aromatics in general, benzene in particular, and olefin (alkene) content. Such regulations led to increasing preference for high octane pure paraffin (alkane) components, such as alkylate, and is forcing refineries to add processing units to reduce benzene content.

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

Environmental Considerations

Combustion of 1 US gallon (3.8 L) of gasoline produces 8,788 grams (19.374 lb) of carbon dioxide (2.3 kg/l), a greenhouse gas. The main concern with gasoline on the environment, aside from the complications of its extraction and refining, is the potential effect on the climate.

Toxicity

The material safety data sheet (MSDS) for unleaded gasoline shows at least 15 hazardous chemicals occurring in various amounts, including benzene (up to 5% by volume), toluene (up to 35% by volume), naphthalene (up to 1% by volume), trimethylbenzene (up to 7% by volume), methyl tert-butyl ether (MTBE) (up to 18% by volume, in some states) and about ten others.

Flammability

Uncontrolled burning of gasoline produces large quantities of soot and carbon monoxide. Like other alkanes, gasoline burns in a limited range of its vapor phase and, coupled with its volatility, this makes leaks highly dangerous when sources of ignition are present. Gasoline has a lower explosion limit of 1.4% by volume and an upper explosion limit of 7.6%. If the concentration is below 1.4%, the air-gasoline mixture is too lean and does not ignite. If the concentration is above 7.6%, the mixture is too rich and also does not ignite. However, gasoline vapor rapidly mixes and spreads with air, making unconstrained gasoline quickly flammable.

Gasoline Production

Gasoline was not invented, it is a natural by-product of the petroleum industry, kerosene being the principal product. Gasoline is produced by distillation, the separating of the volatile, more valuable fractions of crude petroleum. However, what was invented were the numerous processes and agents needed to improve the quality of gasoline making it a better commodity.

The Automobile

When the history of the automobile was heading in the direction of becoming the number one method of transportation there was created a need for new fuels. In the nineteenth century, coal, gas, camphene, and kerosene made from petroleum were being used as fuels and in lamps. However, automobile engines required fuels that needed petroleum as a raw material. Refineries could not convert crude oil into gasoline fast enough as automobiles were rolling off the assembly line.

Cracking

There was a need for improvement in the refining process for fuels that would prevent engine knocking and increase engine efficiency. Especially for the new high compression automobile engines that were being designed. The processes that were invented to improve the yield of gasoline from crude oil were known as cracking. In petroleum refining, cracking is a process by which heavy hydrocarbon molecules are broken up into lighter molecules by means of heat, pressure, and sometimes catalysts. In 1913, thermal cracking was invented by William Meriam Burton, a process that employed heat and high pressures. Eventually, catalytic cracking replaced thermal cracking in gasoline production. Catalytic cracking is the application of catalysts that create chemical reactions, producing more gasoline.