5.3 Why were alkyl lead compounds removed?
Description
This article is from the Gasoline FAQ, by Bruce Hamilton with numerous contributions by others.
5.3 Why were alkyl lead compounds removed?
" With the exception of one premium gasoline marketed on the east coast
and southern areas of the US, all automotive gasolines from the mid-1920s
until 1970 contained lead antiknock compounds to increase antiknock quality.
Because lead antiknock compounds were found to be detrimental to the
performance of catalytic emission control system then under development,
U.S. passenger car manufacturers in 1971 began to build engines designed to
operate satisfactorily on gasolines of nominal 91 Research Octane Number.
Some of these engines were designed to operate on unleaded fuel while others
required leaded fuel or the occasional use of leaded fuel. The 91 RON was
chosen in the belief that unleaded gasoline at this level could be made
available in quantities required using then current refinery processing
equipment. Accordingly, unleaded and low-lead gasolines were introduced
during 1970 to supplement the conventional gasolines already available.
Beginning with the 1975 model year, most new car models were equipped
with catalytic exhaust treatment devices as one means of compliance with
the 1975 legal restrictions in the U.S. on automobile emissions. The need
for gasolines that would not adversely affect such catalytic devices has
led to the large scale availability and growing use of unleaded gasolines,
with all late-model cars requiring unleaded gasoline."[69].
There was a further reason why alkyl lead compounds were subsequently
reduced, and that was the growing recognition of the highly toxic nature of
the emissions from a leaded-gasoline fuelled engine. Not only were toxic
lead emissions produced, but the added toxic lead scavengers ( ethylene
dibromide and ethylene dichloride ) could react with hydrocarbons to produce
highly toxic organohalogen emissions such as dioxin. Even if catalysts were
removed, or lead-tolerant catalysts discovered, alkyl lead compounds would
remain banned because of their toxicity and toxic emissions [70,71].
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