4.7 Why not use other organometallic compounds?
Description
This article is from the Gasoline FAQ, by Bruce Hamilton with numerous contributions by others.
4.7 Why not use other organometallic compounds?
As the toxicity of the alkyl lead and the halogenated scavengers became of
concern, alternatives were considered. The most famous of these is
methylcyclopentadienyl manganese tricarbonyl (MMT), which was used in the
USA until banned by the EPA from 27 Oct 1978 [30], but is approved for use
in Canada and Australia. Recently the EPA ban was overturned, and MMT can
be used up to 0.031gMn/US Gal in all states except California ( where it
remains banned ). The EPA has stated it intends to review the whole MMT
siuation and , if evidence supports removing MMT, they will revisit banning
MMT. Automobile manufacturers believe MMT reduces the effectiveness of the
latest emission control systems [31]. Canada also contemplated banning
MMT because of the same concerns, as well as achieving fuel supply
uniformity with the lower 48 states of the USA [31]. MMT is more expensive
than alkyl leads and has been reported to increase unburned hydrocarbon
emissions and block exhaust catalysts [32].
Other compounds that enhance octane have been suggested, but usually have
significant problems such as toxicity, cost, increased engine wear etc..
Examples include dicyclopentadienyl iron and nickel carbonyl. Germany used
iron pentacarbonyl (Fe(CO)5) at levels of 0.5% or less in gasoline during
the 1930s. While its cost was low, one of its major drawbacks was that the
carbonyl decomposed rapidly when the gasoline was exposed to light. Iron
oxide (Fe3O4) also deposited on the spark plug insulator causing short
circuits, and the precipitation of iron oxides in the lubricating oil also
led to excessive wear rates [33].
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