Environmental Engineering Reference
In-Depth Information
Along with diminishing petroleum reserves, the price of oil and natural gas has
increased dramatically. A barrel of crude oil reached a record high price of $147.27
in July 2008, which is an increase of 1,190% over the $12.38 per barrel price in
July 1998 [4]. Due to the rapid increase in the price of oil, the price per gallon of
regular unleaded gasoline increased from $1.08 in July 1998 to $4.09 in July 2008
[5], representing an increase of 379%. As the price of petroleum increased, so did
corporate profits. Exxon/Mobil reported a second-quarter profit of $11.68 billion in
August 2008, when gas prices were the highest [6].
The concentrations of heat-trapping greenhouse gases in the atmosphere have
significantly increased over the past century due to the burning of fossil fuels, such
as oil and coal, combined with deforestation. As a result, the average temperature
of the Earth's surface is increasing at an alarming rate [7]. The issue of climate
change is one of the key challenges facing us and it is imperative that steps are taken
to reduce greenhouse gas emission. The combination of diminishing petroleum
reserves (it is generally believed that we reached a global “peak” oil or a global
Hubbert's peak in 2006 [8]), and the deleterious environmental consequences of
greenhouse gases has led to an urgent and critical need to develop alternative, renew-
able and environmentally friendly fuels. Examples include biodiesel, biobutanol,
and cellulosic ethanol; the topics of this chapter.
Biodiesel is a renewable, non-toxic [9], biodegradable alternative fuel, which
can be used in conjunction with or as a substitute for petroleum diesel fuel.
Biodiesel is made entirely from vegetable oil or animal fats by the transesterifi-
cation of triglycerides and alcohol in the presence of a catalyst. An advantage is
that compression-ignition (diesel) engines, manufactured within the last 15 years,
can operate with biodiesel/petroleum diesel at ratios of 2% (B2), 5% (B5), or 20%
(B20), and even pure biodiesel (B100), without any engine modifications. Biodiesel
contains no polycyclic aromatic hydrocarbons, and emits very little sulfur dioxide,
carbon monoxide, carbon dioxide, and particulates, which greatly reduces health
risks when compared to petroleum diesel.
Butanol is a four-carbon alcohol that can be produced from petroleum or
biomass, and is currently used as an industrial chemical solvent. Biobutanol is
an advanced biofuel that has an energy density, octane value, Reid vapor pressure
(RVP), and other chemical properties similar to gasoline [10]. Without any engine
modifications, it can either be blended at any ratio with standard grade petroleum
gasoline or used directly as a fuel. Biobutanol can be produced from the fermenta-
tion of sugars from biomass or by the gasification of cellulosic biomass. Compared
to gasoline, the combustion of butanol reduces the amount of hydrocarbons, carbon
monoxide, and smog creating compounds that are emitted [11].
Cellulosic ethanol is ethyl alcohol, a two-carbon straight-chained alcohol, which
is produced from wood, grass, or other cellulosic plant material, particularly the
non-edible portions. Ethanol produced from renewable sources can be used as a
high-octane biodegradable motor fuel, and is clean burning. It can be used in cur-
rent automobile engines in blends up to 10% with gasoline (E10) without any
engine modifications, and in higher percentages (E85 and E100) in Flex Fuel
Vehicles (FFVs). Biomass consists of cellulose, hemicellulose, and lignin, which
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