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Synthetic ethanol
Ethene, produced by the cracking of oil, is converted to ethanol
using steam and a catalyst. The reaction also produces toxic by-products,
so synthetic ethanol is never used for human consumption. A further
purification stage is necessary to remove water and by-products,
and newer methods are making use of safer reagents.
This is the principal method used in the UK
for industrial ethanol. Click here for
more information on this process.
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There are essentially three methods used to
produce ethanol:
- Manufacture from ethene using steam (the
"synthetic" route)
- Production from sugars and starches by fermentation,
using yeasts
- Production from biomass waste, using bacteria.
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Fermented ethanol
Fermentation has been carried out for millennia and is the traditional
method of common alcohol production. Most of the world's ethanol
is produced by fermentation, using crops such as sugar cane, sugar
beet, corn, rice and maize. Municipal waste can also be used as
feedstock, reducing landfill disposal and turning rubbish into
a valuable product.
The fermentation is a complex series of reactions that convert
carbohydrates, mainly sugars and starches, into ethanol and carbon
dioxide. It works best at temperatures in the range 25°C -
37°C in the absence of oxygen (anaerobic), and will produce
aqueous solutions of up to 14% ethanol. Higher alcohol contents
require further distillation.
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To find out more about production by ethanol
fermentation, click here.
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Biotechnology
Recent advances in biotechnology have led to the development of
a process to produce ethanol from waste biomass using bacteria.
Genetically engineered E-coli bacteria are used to convert plant
sugars into ethanol, rather than to ethanoic or lactic acid as
usually happens.
This allows ethanol to be processed from forestry waste, rice
hulls, sugar cane residues (called "bagasse"), and the
main crop can be grown as a food source. It is expected that in
time ethanol will be able to compete economically with fossil
fuels, removing the need for an ethanol fuel subsidy.
The use of waste to produce ethanol may also help solve the problem
of disposal that has arisen since many places have begun to ban
burning crop residues because of environmental concerns over its
impact, or where ploughing-in waste is not possible because of
the soil type.
Click here for more on producing ethanol
from waste biomass.
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