GASOLINE

Gasoline, also called gas (United States and Canada) or petrol (Great Britain), or benzine (Europe), is a mixture of volatile, flammable liquid hydrocarbons derived from petroleum and used as fuel for internal-combustion engines.

The hydrocarbons in gasoline boil below 180 C (355 F) or, at most, below 200 C (390 F). The hydrocarbon constituents in this boiling range are those that have 4 to 12 carbon atoms in their molecular structure and are classified into three general types: paraffins (including the cycloparaffins and branched materials), olefins, and aromatics.

Highly branched paraffins, which are particularly valuable constituents of gasolines, are not usually the principal paraffinic constituents of straight-run gasoline. The more predominant paraffinic constituents are usually the normal (straight-chain) isomers, which may dominate the branched isomers by a factor of 2 or more. This is presumed to indicate the tendency to produce long uninterrupted carbon chains during petroleum maturation rather than those in which branching occurs.

Gasoline is manufactured by distillation in which the volatile, more valuable fractions of crude petroleum are separated. Later processes, known as cracking, were designed to raise the yield of gasoline from crude oil by converting the higher-molecular-weight constituents of petroleum into lower-molecular-weight products Other methods used to improve the quality of gasoline and increase its supply include polymerization, alkylation, isomerization, and reforming.

Polymerization is the conversion of gaseous olefins, such as propylene and butylene, into larger molecules in the gasoline range. Alkylation is a process combining an olefin and a...