Environmental Engineering Reference
In-Depth Information
Chapter IV
B IOFUELS
The worldwide depletion of fossil fuels and widespread concern over increasing
atmospheric CO2 have sparked interest not only in biomaterials but also in sustainable, non-
fossil-based fuels. Political instability in petroleum-producing regions has further increased
the desirability of domestic fuel sources, particularly for transportation [1]. Solar and wind
power are well-suited to sustainable generation of electricity, including electricity for
charging vehicle batteries, but most modern vehicles are designed for liquid fuels that are best
simulated by two biofuels: bioethanol and biodiesel [2]. In addition, biohydrogen is an
emerging biofuel that carries energy from sunlight or organic matter, rather than petroleum, in
clean-burning hydrogen (H 2 ), Finally, biodesulfurization of petroleum products may offer a
way to mitigate some effects of petroleum use during a transition and is discussed as well.
A. B IOETHANOL
1. Introduction
Proponents of ethanol as a use for fuel highlight the apparent net-zero contribution of fuel
ethanol combustion to the global carbon cycle, in that feedstocks for ethanol production
derive their carbon from atmospheric CO 2 , and that ethanol combustion simply returns the
fixed carbon to its atmospheric source [3]. Others, however, make the valid counterpoints that
the conversion even of agricultural wastes to ethanol is, itself, an energy-intensive process
that frequently makes use of fossil energy sources, and that growth of crops dedicated to
energy production must also be conducted in a sustainable manner for fuel ethanol use to
carry a net environmental benefit [4].
Petroleum currently supplies 97 percent of the energy consumed for transportation [5],
and transportation accounted for two-thirds of U.S. petroleum use in 2002. This trend is
expected to continue until 2025 [6]. This need not continue, however, as all automobile
manufacturers produce flexible-fuel vehicles (FFVs) that can use 10 percent or 85 percent
ethanol blends with gasoline, and ethanol can also replace diesel fuel in heavy vehicles [5].
The United States also now has 199 fueling stations for ethanol, as well as extensive online
services for planning travel between stations [7]. Although ethanol is limited in availability in
some states, the transportation market for ethanol could expand to as much as 3 8-53 billion
liters per year, if all available agricultural residues were converted to ethanol [8]. Ethanol is
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