Cellulosic ethanol - Wikipedia, the free encyclopedia
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Cellulosic ethanol
From Wikipedia, the free encyclopedia
Cellulosic ethanol is a blend of normal ethanol that can be produced from a great diversity of biomass including
waste from urban, agricultural, and forestry sources. There are at least two methods of production of cellulosic
ethanol—enzymatic hydrolysis and synthesis gas fermentation. Neither process generates toxic emissions when it
produces ethanol. The technology is very new and exists in pilot configurations where testing is ongoing.
According to US Department of Energy studies
(http://www.eere.energy.gov/biomass/news_detail.html/news_id=9332/) conducted by the Argonne Laboratories of
the University of Chicago, one of the benefits of cellulosic ethanol is that it reduces greenhouse gas emissions (GHG)
by 85% over reformulated gasoline. By contrast, sugar-fermented ethanol reduces GHG emissions by 18% to 29%
over gasoline.
In April 2004, Iogen Corporation, a Canadian biotechnology firm, became the first business to commercially sell
cellulosic ethanol. The primary consumer thus far has been the Canadian government, which, along with the United
States government (particularly the Department of Energy's National Renewable Energy Laboratory), has invested
millions of dollars into assisting the commercialization of cellulosic ethanol.
Genencor (http://www.genencor.com/) and Novozymes (http://www.novozymes.com/) are two other companies that
have received United States government Department of Energy funding for research into reducing the cost of
cellulase, a key enzyme in the production cellulosic ethanol by enzymatic hydrolysis.
Other enzyme companies such as Dyadic International, Inc. (AMEX: DIL) (http://www.dyadic-group.com/) have
been using fungi to develop and manufacture cellulases in 150,000 liter industrial fermenters since 1994. With the
advent of genetic engineering and genomics companies like Dyadic, Genencor and Novozymes have the modern
biological tools such as Dyadic's patented C1 Host Technology [1] (http://www.dyadicgroup.com/pdf/dyadic_article_in_GEN_Aug2004.pdf) to develop and manufacture large volumes of new and better
performing enzyme mixtures to make the production of cellulosic ethanol more economical.
BRI Energy, LLC (http://www.brienergy.com/) is a company whose pilot plant in Fayetteville, Arkansas is currently
using synthesis gas fermentation to convert a variety of waste into ethanol. After gasification, anaerobic bacteria
(Clostridium ljungdahlii) are used to convert the syngas (CO, CO2, and H2) into ethanol. The heat generated by
gasification is also used to co-generate excess electricity.
President Bush, in his State of the Union address delivered January 31, 2006, proposed to expand the use of cellulosic
ethanol.
Contents
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1 Production methods
„ 1.1 Hydrolysis processes
„ 1.2 Chemical hydrolysis
„ 1.3 Enzymatic Hydrolysis
„ 1.4 Gasification process
2 Economic importance
3 References
Production methods
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Cellulosic ethanol - Wikipedia, the free encyclopedia
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There are two broad ways of producing alcohol from cellulose. Hydrolysis breaks down the cellulose chains into
sugar molecules that are then fermented and distilled. Gasification transforms the carbon in the raw material into a
gaseous carbon monoxide that is then fed to a special kind of fermenter.
Hydrolysis processes
The cellulose molecules are composed of long chains of beta-glucose molecules. In the hydrolysis process, these
chains are broken down to "free" the sugar, before feeding it to a fermenter for alcohol production. There are four or
five stages in the process:
1.
2.
3.
4.
5.
An optional "pre-treatment" phase, to make the raw material such as wood or straw amenable to hydrolysis,
Hydrolysis, to break down the molecules of cellulose into sugars;
Separation of the sugar solution from the residual materials, notably lignin;
Fermentation of the sugar solution;
Distillation to produce 99.5% pure alcohol.
There are two major hydrolysis processes: a chemical reaction using acids, or an enzymatic reaction.
Chemical hydrolysis
In the traditional methods (http://journeytoforever.org/biofuel_library/wood_alcohol.html) developed in the 19th
century and at the beginning of the 20th century, hydrolysis is performed by attacking the cellulose with an acid under
high heat and high pressure. Modern variations of this technique are being explored by companies such as Arkenol
(http://www.arkenol.com/) or BC International Corporation (http://www.bcintlcorp.com/).
Enzymatic Hydrolysis
Cellulose chains can be broken into beta-glucose atoms by the cellulase enzyme. This reaction occurs at body
temperature in the stomach of ruminants, where the enzyme are produced by bacteria—there are actually at least three
enzymes, used at various stages of the conversion. The enzymatic hydrolysis process depends on a steady supply of
the cellulase enzymes.
The IOGEN corporation is a Canadian producer of enzymes. They are promoting an enzymatic hydrolysis process
(http://www.iogen.ca/cellulose_ethanol/what_is_ethanol/process.html) that uses "specially engineered enzymes". The
raw material (wood or straw) has to be pre-treated to make it amenable to hydrolysis.
Genencor (http://www.genencor.com/) and Novozymes (http://www.novozymes.com/) are two other companies that
have received United States government Department of Energy funding for research into reducing the cost of
cellulase, a key enzyme in the production cellulosic ethanol by enzymatic hydrolysis.
Other enzyme companies such as Dyadic International, Inc. (AMEX: DIL) (http://www.dyadic-group.com/) have
been using fungi to develop and manufacture cellulases in 150,000 liter industrial fermenters since 1994. With the
advent of genetic engineering and genomics companies like Dyadic, Genencor and Novozymes have the modern
biological tools such as Dyadic's patented C1 Host Technology [2] (http://www.dyadicgroup.com/pdf/dyadic_article_in_GEN_Aug2004.pdf) to develop and manufacture large volumes of new and better
performing enzyme mixtures to make the production of cellulosic ethanol more economical.
Gasification process
The gasification process of the BRI Energy (http://www.brienergy.com/index.html) company does not rely on
chemical decomposition of the cellulose chain. Instead of breaking the cellulose into sugar molecules, the carbon in
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the raw material is converted into carbon monoxide, using what amounts to partial combustion. The carbon monoxide
is then fed into a special kind of fermenter. Instead of yeast, which operates on sugar, their process uses a
microorganism named “Clostridium ljungdahlii”. This microorganism will ingest (eat) carbon monoxide and produce
ethanol, hydrogen and water. The process can thus be broken into three steps:
1. Gasification — Complex carbon based molecules are broken apart to access the carbon as carbon monoxide
2. Fermentation — Convert the carbon monoxide into ethanol using the Clostridium ljungdahlii organism
3. Distillation — Ethanol is separated from hydrogen and water
Economic importance
The quest for alternative energies has provided many ways to produce electricity, such as wind farms, hydropower, or
solar cells. However, about 40% of the total energy consumption is dedicated to transports and in practice requires
liquid fuels such as gasoline, diesel fuel, or kerosene. These fuels are all obtained by refining petroleum. This
dependency on oil has two major drawbacks: burning fossil fuels such as oil contributes to global warming; and
importing oil creates a dependency on oil producing countries. Ethanol fuel is a practical alternative to oil.
Ethanol, today, is produced mostly from sugars or starches, obtained from fruits and grains. In contrast, cellulosic
ethanol is obtained from cellulose, the main component of wood, straw and much of the plants. Since cellulose cannot
be digested by humans, the production of cellulose does not compete with the production of food. The price per ton of
the raw material is thus much cheaper than grains or fruits. Moreover, since cellulose is the main components of
plants, the whole plant can be harvested. This results in much better yields per acre—up to 10 tons, instead of 4 or 5
tons for the best crops of grain.
The raw material is plentiful. Cellulose is present in every plant: straw, grass, wood. Most of these "bio-mass"
products are currently discarded. Transforming them into ethanol might provide as much as 30% of the current fuel
consumption in the US—and probably similar figures in other oil-importing regions like China or Europe. Moreover,
even land marginal for agriculture could be planted with cellulose producing crops like switchgrass, resulting in
enough production to substitute for all the current oil imports.
References
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US DOE page on cellulosic ethanol production via enzymatic hydrolysis
(http://www.eere.energy.gov/biomass/enzymatic_hydrolysis.html)
US DOE page on cellulosic ethanol production via synthesis gas fermentation
(http://www.eere.energy.gov/biomass/synthesis_gas_fermentation.html/)
2006 State Of The Union speech mentioning use of renewable fuels
(http://www.whitehouse.gov/stateoftheunion/2006/)
Rocky Mountain Institute page on ethanol (http://www.rmi.org/sitepages/pid1157.php)
The "Wood-Ethanol Report" (http://www.journeytoforever.org/biofuel_library/WoodEthanolReport.html) by
Environment Canada, 1999, re-published by the Journey to Forever (http://www.journeytoforever.org/) web
site.
www.carbohydrateeconomy.org
(http://www.carbohydrateeconomy.org/library/admin/uploadedfiles/How_Much_Energy_Does_it_Take_to_Mak
Ethanol energy balance calculations concluding a net energy ratio of 2.62:1 for state of the art cellulosic crop
end-to-end production.
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