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Gasolines with an octane rating that satisfies market requirements are produced
in refineries by blending various refinery streams that differ in composition,
boiling range and octane ratings.
The octane number is an expression of the antiknock property of gasoline and
is defined as the percentage, by volume, of isooctane (assigned an octane number
of 100) that must be mixed with n-heptane (assigned an octane number of 0)
in order to match the knock intensity of the fuel that is undergoing test.
Until recently, methyl tertiary-butyl ether (MTBE) was the predominant oxygenate
used worldwide; however, a major shift to alternative oxygenates such as ethyl
alcohol (ethanol) and ETBE is starting to occur. These oxygenates are projected
to replace MTBE and become the oxygenate of choice in some regions. A number
of factors have led to this transformation. In the United States, environmental
and health concerns regarding MTBE water contamination have spurred legislation
to ban MTBE and to turn to more environmentally friendly and renewable fuels.
Unlike the United States, European MTBE use will not decline as a result of
environmental or health reasons, but because of increased replacement by ETBE,
which has been driven by tax laws and economic benefits. In Asia, although
there is still uncertainty regarding MTBE use in most countries, ethanol is
being introduced as a comparable replacement. World consumption of MTBE was
about 17.5 million metric tons in 2004. The following pie chart shows world
consumption of MTBE by country or region:
Ethanol has been used as a blending agent in motor fuels in some countries
since the 1950s, but its use as an octane improver has not been as widespread
until recently. In the United States, the newly introduced Energy Policy Act
of 2005 encourages and supports the use of ethanol, and its consumption will
continue to grow significantly as it replaces MTBE. In 2005, ethanol overtook
MTBE as the primary oxygenate used in the United States and will dominate the
market by 2010. Although fuel ethanol use is still being studied in Europe,
it is expected that growth will be significant in the next few years, and that,
combined with ETBE, it will replace MTBE to a degree. In Asia, some countries
have already regulated MTBE and are using ethanol as a replacement. For example,
Thailand and India are beginning to replace MTBE with ethanol-blended gasoline.
Also, significant growth for fuel ethanol use (over 7% annually) is expected
for China and India in the next few years.
Ethyl tertiary-butyl ether (ETBE) is also used to improve octane or fulfill
oxygenate requirements. As mentioned, ETBE is increasingly being produced and
consumed in Western Europe. It is economical there because tax exemptions help
compensate for its higher cost compared with MTBE. In the next few years, it
is expected that ETBE for oxygenate purposes will overtake MTBE as the primary
oxygenate used in Western Europe. Unlike Western Europe, the United States
has negligible production and consumption of ETBE. Most of its ETBE plants
are configured to produce the less-expensive MTBE product. Also, there is concern
that ETBE shares similar environmental and health hazards as MTBE and that,
without liability protection for producers, ETBE production and consumption
will not be feasible in the future. Although Japan is now considering using
ETBE starting in 2010, no significant amounts of ETBE are currently used in
Asia.
The shift from MTBE to other oxygenates such as ethanol and ETBE is significant
because it is occurring in regions (the United States and Western Europe) where
oxygenates are traditionally heavily used. However, MTBE use will continue
and even increase in other parts of the world. For example, while significant
declines or nongrowth will occur in the Americas or in Western Europe, other
regions such as Asia, the Middle East, and Central and Eastern Europe will
increase MTBE use, pending future legislation and government decisions.
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