World Energy Outlook 2006

not require engine modifications and can be supplied in the same way as
gasoline through existing retail outlets. Higher-percentage blends, with more
than 30% ethanol, or pure ethanol can be used only with some modifications
to the vehicle engine. Ethanol has a high octane value, which makes it an
attractive gasoline-blending component. It has generally good performance
characteristics, though its energy content by volume is only two-thirds that of
gasoline. The higher volatility of ethanol can create problems, especially in the
summer months. Demand for ethanol as an octane enhancer is rising in several
countries, especially the United States, where methyl-tertiary-butyl-ether
(MTBE) – the most commonly used oxygenate – is being phased out or
discouraged for health and environmental reasons. The fuel economy of a
vehicle with an engine modified to run on pure ethanol, measured by
kilometres per litre, can approach that of a gasoline-only version of the same
vehicle, despite ethanol’s lower energy content. 5 In several countries, “flex-fuel”
vehicles, which allow consumers to switch freely between high-proportion
ethanol blends and gasoline, have recently become available. This insulates the
consumer from any sudden jump in the price of ethanol relative to gasoline
that might result from a supply shortage or a drop in gasoline prices.
Ethanol production is rising rapidly in many parts of the world in response to
higher oil prices, which are making ethanol more competitive, especially where
reinforced by government incentives and rules on fuel specifications. Global
production reached 17.1 Mtoe (579 kb/d) in 2005, almost double the level of
2000 (Figure 14.2). The United States accounted for much of the increase in
output over that period. In most cases, virtually all the ethanol produced is
consumed domestically, though trade is growing rapidly. Brazil accounts for
half of global trade in ethanol (see below).
Biodiesel
The most well-established technology for biodiesel production is the
transesterification of vegetable oils or animal fats. The process involves filtering
the feedstock to remove water and contaminants, and then mixing it with an
alcohol (usually methanol) and a catalyst (usually sodium hydroxide or
potassium hydroxide). This causes the oil molecules (triglycerides) to break
apart and reform into esters (biodiesel) and glycerol, which are then separated 14
5. This depends on whether the engine is optimised to run on ethanol. The high octane number of
ethanol-rich blends, plus the cooling effect from ethanol’s high latent heat of vaporisation, allows a
higher compression ratio in engines designed for ethanol-rich blends. This is especially the case for
vehicles using direct-injection systems. These characteristics result in increased horsepower and can
partially offset the lower energy content of ethanol vis-à-vis gasoline.
Chapter 14 - The Outlook for Biofuels
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