ABSTRACT
Carbon dioxide accumulation in the atmosphere is a major contributor to global warming and climate change. When bioethanol is used instead of gasoline as an automobile fuel, C 0 2 emissions are reduced by 90% (Tyson et al., 1993). However, ethanol from biomass reduces net C 0 2 emissions since fermentation C 0 2, produced during ethanol production, is part of the global carbon cycle (Wyman, 1994). There is also potential to use ethanol as oxy genate to replace methyl tert-butyl ether (MTBE) in its capacity to reduce CO emissions by improving oxidative combustion (Blackburn et al., 1999; Unnasch et al., 2001). A disadvantage of ethanol is that it has only 65-69% of the energy density of hydrocarbon fuels (Lynd, 1996). Com ethanol is being used to supplement gasoline at a rate of up to 10% in the United States and Canada, supported by tax incentives. For example, the US highway bill in cludes an extension to the ethanol tax incentive program to 2007, which adds about SOc-gal·1 to the value of ethanol for the fuel market, allowing ethanol to sell for US$ 1.20-1.40-gal·1 (Sheehan and Himmel, 1999). Ulti mately, technological developments must be such as to eliminate the need for the tax incentive. Brazil is the only other country that produces large quantities of fuel ethanol-in this case, from sugarcane. In fact, the first major fuel-ethanol program (ProAlcool) started in Brazil in 1975, followed by programs in the USA in 1978 and more recently in Canada (Wheals et al., 1999). However, as in North America, only tax credits make fuel ethanol commercially viable.
