Environmental Engineering Reference
In-Depth Information
Methanol is currently produced from natural gas by steam reforming process
and is distributed primarily as an industrial chemical, but it could be produced also
by any carbonaceous material including biomass. It has many desirable combus-
tion and emissions characteristics, such as higher octane number and wider
flammability limits (lean combustion capability) than gasoline, in addition being a
liquid its storage and handling are much simpler than gaseous fuels. Light duty
methanol vehicles have NO x and CO emissions similar to gasoline vehicles, while
light hydrocarbons emissions are about half those gasoline vehicles. Emissions of
formaldehyde (a primary combustion product of methanol) are much higher with
respect to those of vehicles fueled by gasoline or other alternative fuels, but can be
easily controlled by exhaust catalytic converters. Its H/C ratio is higher than
gasoline or Diesel fuel, therefore it produces less CO 2 when burned. However,
methanol presents some serious limitations as motor fuel, in particular it is highly
toxic and corrosive, its energy density is lower than that of gasoline due to the high
atomic weight of the oxygen contained in its molecule, its mass heating energy is
about half with respect to gasoline. The most common methanol fuel is the blend
M85, containing 15% of gasoline, which solves the cold start problems of meth-
anol, due to its volatility.
Since oil crisis of 1970, the potential use of fuels deriving from renewable
sources has been studied and proposed. In this perspective ethanol produced by
biomass (bioethanol) has received the major attention. Due to the fact that
bioethanol is produced from plants, its burning would lead to a complete recy-
clable carbon dioxide. It can be obtained by fermentation techniques from any
carbohydrate-containing materials, in particular from several types of cereals,
sugarcane, sugarbeet, and wood. Brazil and USA are the largest producers of
ethanol (two-third of the total worldwide production), obtained from sugarcane
and corn, respectively, while the contribution of Europe is lower than 10% (mainly
from sugarbeet). About 80% of the ethanol produced worldwide is utilized in the
transportation sector, where it is most commonly used as an oxygenate in blends
with gasoline, which can be burned in conventional spark ignition engines, while
specialized engines would be necessary to burn pure ethanol. In Brazil, the pro-
portion of bioethanol in gasoline is about 25% (''gasohol''), while in USA and
Europe concentrations of 10 and 5% are admitted, respectively. The main effect of
using ethanol in blend with gasoline consists in slightly lower emissions of light
hydrocarbons and CO. The possibility of using much higher concentrations of
ethanol has been permitted by the recent developments of the so-called ''flexible
fuel vehicles'' (FFVs), which are able to run with any mixture of gasoline and
ethanol up to a concentration of 85% ethanol (E85 fuel). In these vehicles, the
oxygen content of the fuel is monitored by sensors, in order to adjust all engine
parameters accordingly. As ethanol has no lubricant properties, its use as stand
alone fuel requires the adoption of additives to ensure the necessary lubricity of the
fuel. These vehicles have reached a large diffusion in Brazil, where about 80% of
new cars utilize the FFV technology. A large use of bioethanol in FFVs could
enable several countries to achieve their targets for CO 2 emission reduction,
however, since ethanol is mainly derived from grains and sugars, its production for
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