fuel is an alternative to gasoline. It can
be combined with gasoline in any concentration up to
pure ethanol (E100). Anhydrous ethanol,
that is, ethanol with at most 1% water, can be blended
with gasoline in varying quantities to reduce consumption
of petroleum fuels and in attempts to reduce air pollution.
Worldwide automotive, ethanol capabilities vary widely
and most spark-ignited gasoline style engines will operate
well with mixtures of 10% ethanol (E10).
In Brazil, ethanol-powered and flexible-fuel vehicles
are manufactured to be capable of operation by burning
hydrated ethanol, an azeotrope of ethanol (around 93%
v/v) and water (7%). Hydrated ethanol may also be mixed
with gasoline in flexible fuel vehicles but a minimum
amount of ethanol (granted by legally regulated gasoline
type C) is required to avoid problems with the mixture.
A few flexible-fuel systems, like Hi-Flex, used by Renault
Clio and Fiat Siena, can also run with pure gasoline.
Ethanol is increasingly used as an oxygenate additive
for standard gasoline, as a replacement for methyl t-butyl
ether (MTBE), the latter chemical being difficult to
retrieve from groundwater and soil contamination. At
a 10% mixture, ethanol reduces the likelihood of engine
knock, by raising the octane rating. The use of 10%
ethanol gasoline is mandated in some cities where the
possibility of harmful levels of auto emissions are
possible, especially during the winter months. Ethanol
can be used to power fuel cells, and also as a feed
chemical in the transesterification process for biodiesel.
can be mass-produced by fermentation of sugar or by
hydration of ethylene from petroleum and other sources.
Current interest in ethanol lies in production derived
from crops (bio-ethanol), and there's discussion about
whether it is a sustainable energy resource that may
offer environmental and long-term economic advantages
over fossil fuels, like gasoline or diesel. It is readily
obtained from the starch or sugar in a wide variety
of crops. Ethanol fuel production depends on availability
of land area, soil, water, and sunlight.
In 2004, around 42 billion
liters of ethanol were produced in the world, most of
it being for use in cars. Brazil produced around 16.4
billion liters and used 2.7 million hectares of land
area for this production, or 4.5% of Brazilian land
area used for crop production in 2005. Around 12,4 billion
liters were produced as fuel to ethanol-powered vehicles
in domestic market.
in South Africa
By using renewable energy sources, like ethanol
from sugarcane & hydroelectricity, Brazil
has reduced its dependence on foreign oil.
is obtained from the conversion of carbon based feedstock.
Agricultural feedstocks are considered renewable because
they get energy from the sun using photosynthesis. Ethanol
can be produced from a variety of feedstocks such as
sugar cane, bagasse, miscanthus, sugar beet, sorghum,
grain sorghum, switchgrass, barley, hemp, kenaf, potatoes,
sweet potatoes, cassava, sunflower, fruit, molasses,
whey or skim milk, corn, stover, grain, wheat, wood,
paper, straw, cotton, other biomass, as well as many
types of cellulose waste. As of 2006, production is
primarily from sugarcane, maize (corn) and sugar beets
- and also as of 2006, technology does not yet exist
that makes it economically competitive to produce ethanol
from cellulosic feedstock.
Four countries have developed bioethanol fuel programs:
Brazil, Colombia, China and the United States.
One result of increased use of ethanol is increased
demand for the feedstocks. Large-scale production of
agricultural alcohol may require substantial amounts
of cultivable land with fertile soils and water. This
may lead to environmental damage such as deforestation
or decline of soil fertility due to reduction of organic
About 5% (in 2003) of the ethanol produced in the world
is actually a petroleum product. It is made by the catalytic
hydration of ethylene with sulfuric acid as the catalyst.
It can also be obtained via ethylene or acetylene, from
calcium carbide, coal, oil gas, and other sources. Two
million tons of petroleum-derived ethanol are produced
annually. The principal suppliers are plants in the
United States, Europe, and South Africa. Petroleum derived
ethanol (synthetic ethanol) is chemically identical
to bio-ethanol and can be differentiated only by radiocarbon
can be produced in different ways, using a variety of
feedstocks. Brazil uses sugarcane as primary feedstock.
For information on Brazil's method of ethanol production,
see ethanol fuel in Brazil. More than 90% of the ethanol
produced in the U.S. comes from corn (see Renewable
Fuels Association's list of United States ethanol plants).
with higher yields of energy, such as switchgrass and
sugar cane, are more effective in producing ethanol
than corn. The production of Ethanol from corn has been
driving up the price of corn creating cost problems
for tortilla makers in Mexico. The Mexican Government
is attempting to reduce the fears of both producers
and consumers over how to best control the rising price
of the centuries-old dietary staple. Some lawmakers
argue that price controls which have worked in the past,
are the best method, while others would like to see
increased production of the alternative resource. Ethanol
can also be produced from sweet sorghum, a dryland crop
that uses much less water than sugarcane, does not require
a tropical climate and produces food and fodder in addition
to fuel. Sweet sorghum cultivar improvement and cultivation
is emphasized in India.
Basic steps for dry mill production of ethanol from
corn are: refining into starch, liquification and saccharification
(hydrolysis of starch into glucose), yeast fermentation,
distillation, dehydration (required for blending with
gasoline), and denaturing (optional).
Ethanol is produced by yeast fermentation of the sugar
extracted from sugarcane or sugar beets. Subsequent
processing is the same as for ethanol from corn. Production
of ethanol from sugarcane (sugarcane requires a tropical
climate to grow productively) returns about 8 units
of energy for each unit expended compared to corn which
only returns about 1.34 units of fuel energy for each
unit of energy expended. Thus sugarcane nets 7/.34 or
about 20 times as much energy as corn. (corn produces
an additional 0.33 units of energy in the form of high-protein
Carbon dioxide, a potentially harmful greenhouse gas,
is emitted during fermentation. However, the net effect
is offset by the uptake of carbon gases by the plants
grown to produce ethanol. When compared to gasoline,
ethanol releases less greenhouse gases.
For the ethanol to be usable as a fuel, water must be
removed. Most of the water is removed by distillation,
but the purity is limited to 95-96% due to the formation
of a low-boiling water-ethanol azeotrope. The 96% m/m
(93% v/v) ethanol, 4% m/m (7% v/v) water mixture may
be used as a fuel, and it's called hydrated ethyl alcohol
fuel (álcool etílico hidratado combustível, or AEHC
in Portuguese). In 2006/2007, an estimated 17 billion
liters (4,5 billion gallons) of hydrated ethyl alcohol
fuel will be produced, to be used in ethanol powered
For blending with gasoline, purity of 99.5 to 99.9%
is required, depending on temperature, to avoid separation.
Currently, the most widely used purification method
is a physical absorption process using molecular sieves.
Another method, azeotropic distillation, is achieved
by adding the hydrocarbon benzene which also denatures
the ethanol (so no extra methanol/petrol/etc. is needed
to render it undrinkable for duty purposes). However,
benzene is a powerful carcinogen and so will probably
be illegal for this purpose soon.
Biotechnology may improve the energy gain of bioethanol.
Ethanol is not typically transported by pipeline for
three reasons. Current production levels will not support
a dedicated pipeline. The costs of building and maintaining
a pipeline from Midwestern United States to either coast
are prohibitive. Any water which penetrates the pipeline
will be absorbed by the ethanol, diluting the mixture.
vehicles with current (2006) design flexible fuel engines,
fuel economy (measured as miles per gallon (MPG), or
liters per 100 km) is directly proportional to energy
content. Ethanol contains approx. 34% less energy per
gallon than gasoline, and therefore will result in a
34% reduction in miles per gallon. For E10 (10% ethanol
and 90% gasoline), the effect is small (~3%) when compared
to conventional gasoline, and even smaller (1-2%) when
compared to oxygenated and reformulated blends. However,
for E85 (85% ethanol), the effect becomes significant.
E85 will produce approximately 27% lower mileage than
gasoline, and will require more frequent refueling.
Actual performance may vary depending on the vehicle.
reduced fuel economy should be considered when making
price comparisons. For example, if regular gasoline
costs $3.00 per gallon, and E85 costs $2.19 per gallon,
the prices are essentially equivalent. If the discount
for E85 is less than 27%, it actually costs more per
mile to use. For USA price comparisons, see.
Some researchers are working to increase fuel efficiency
by optimizing engines for ethanol-based fuels. Ethanol's
higher octane allows an increase of an engine's compression
ratio for increased thermal efficiency. In one study,
complex engine controls and increased exhaust gas recirculation
allowed a compression ratio of 19.5 with fuels ranging
from neat ethanol to E50. Thermal efficiency up to approximately
that for a diesel was achieved. This would result in
the MPG of a dedicated ethanol vehicle to be about the
same as one burning gasoline. There are currently no
commercially-available vehicles that make significant
use of ethanol-optimizing technologies, but this may
change in the future.