| What is MTBE
At room temperature,
MTBE is a volatile, flammable, and colorless liquid that is highly
soluble in water and has a strong odor. It is manufactured by the
chemical reaction of methanol, generally made from natural gas,
and isobutylene. MTBE has an oxygen atom bonded to two carbon atoms.
One carbon atom is that of a methyl group, -CH3, and
the other is the central atom of a tertiary butyl group, -C(CH3)3.
How
is MTBE used
MTBE has been used in gasoline since 1979. Initially
it was added to increase the octane (the measure of a gasoline's
ability to resist engine knock) of gasoline. It the late 1980's.
it began to be used in California to help reduce tailpipe emissions
particularly those of older vehicles which could not use unleaded
gasoline. In 1990, Congress enacted the Clean Air Act Amendments.
Early versions of the legislation contained a provisions that would
have required the introduction of alternative (non- petroleum) fuels
to reduce the emissions from vehicles which are a significant contributor
to air pollution and ozone. However, because existing vehicles would
not be able to use these alternative fuels, there was concern that
the alternative fuel requirement would not achieve immediate significant
emission reductions. As a result, the final legislation substituted
a requirement for reformulated gasoline (``RFG"). Under this mandate,
RFG would have to contain oxygenates. Adding oxygenates to gasoline
increases the amount of oxygen in the fuel and cuts down on carbon
monoxide and other toxic air emissions. Since all vehicles could
use this fuel, it was believe that immediate air quality benefits
could be achieved. The
Oxyfuel Program requires the use of gasoline with 2.7- percent oxygen
(by weight) in areas with high levels of carbon monoxide during
the fall and winter. When MTBE is used to meet this requirement,
it is used at a concentration of 15 percent (by volume) in gasoline.
Because ethanol has a higher oxygen content, it can meet this requirement
with a concentration of 7.3 percent (by volume). Oxygenated fuels
are used in EPA's winter oxygenated fuels program in twenty-five
areas of the country.
The RFG Program requires 2.0-percent oxygen (by weight) throughout
the year in the most polluted metropolitan areas. MTBE meets this
level with an 11- percent (by volume) concentration, and ethanol
can be used with a 5.4-percent (by volume) concentration .
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