4.4.2 Unsaturated Hydrocarbons
Description
This article is from the Gasoline FAQ, by Bruce Hamilton with numerous contributions by others.
4.4.2 Unsaturated Hydrocarbons
- Unstable, are the remaining component of gasoline.
- Tend to burn in air with a smoky flame.
Alkenes ( aka olefins, have carbon=carbon double bonds )
- These are unstable, and are usually limited to a few %.
- tend to be reactive and toxic, but have desirable octane ratings.
C
| C5H10
2-methyl-2-butene C-C=C-C
Alkynes ( aka acetylenes, have carbon-carbon triple bonds )
- These are even more unstable, are only present in
trace amounts, and only in some poorly-refined gasolines.
Acetylene C=C C2H2
Arenes ( aka aromatics )
- Used to be up to 40%, gradually being reduced to <20% in the US.
- tend to be more toxic, but have desirable octane ratings.
- Some countries are increasing the aromatic content ( up to 50% in some
super unleaded fuels ) to replace the alkyl lead octane enhancers.
C C
// \ // \
C C C-C C
Benzene | || Toluene | ||
C C C C
\\ / \\ /
C C
C6H6 C7H8
Polynuclear Aromatics ( aka PNAs or PAHs )
- These are high boiling, and are only present in small amounts in gasoline.
They contain benzene rings joined together. The simplest, and least toxic,
is Naphthalene, which is only present in trace amounts in traditional
gasolines, and even lower levels are found in reformulated gasolines.
The larger multi-ringed PNAs are highly toxic, and are not present in
gasoline.
C C
// \ / \\
C C C
Naphthalene | || | C10H8
C C C
\\ / \ //
C C
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