Cellulosic ethanol

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Cellulosic ethanol is the type of ethanol that is produced from a great diversity of biomass including waste from urban, agricultural, and forestry sources. Unlike normal ethanol, whose original raw material are sugars and starches, cellulosic ethanol starting raw material is cellulose. There are at least two methods of production of cellulosic ethanol — hydrolysis followed by fermentation of the generated free sugars and synthesis gas fermentation or catalysis (e.g., Fischer Tropsch). 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 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, starch ethanol (e.g., from corn), which uses most of the time natural gas to provide energy for the process, reduces GHG emissions by 18% to 29% over gasoline. Sugar ethanol, on the other hand, from sugarcane, reduces greenhouse gas emissions by as much as cellulosic ethanol because it uses sugarcane bagasse to provide the energy for the process and the excess to make electricity for the grid.

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.

Another company which appears to be nearing commercialization of cellulosic ethanol is Spain's Abengoa Bioenergy. Abengoa has and continues to invest heavily in the necessary technology for bringing cellulosic ethanol to market. They are building a 5 million gallon cellulosic ethanol facility in Spain and have recently entered into a strategic research and development agreement with Dyadic International, Inc. (AMEX: DIL), to create new and better enzyme mixtures which may be used to improve both the efficiencies and cost structure of producing cellulosic ethanol.

President Bush, in his State of the Union address delivered January 31, 2006, proposed to expand the use of cellulosic ethanol.

1 Production methods
- 1.1 Hydrolysis processes
  - 1.1.1 Chemical hydrolysis
  - 1.1.2 Enzymatic Hydrolysis
- 1.2 Gasification process
2 Economic importance and viability
3 References
4 External links
5 See also

[edit] Production methods

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 lignocellulosic raw material into gaseous carbon monoxide and hydrogen that is then fed to a special kind of fermenter or to a catalyst bed.

[edit] Hydrolysis processes

The cellulose molecules are composed of long chains of glucose molecules. In the hydrolysis process, these chains are broken down to "free" the sugar, before it is fermented for alcohol production. There are two major hydrolysis processes: a chemical reaction using acids, or an enzymatic reaction.

[edit] Chemical hydrolysis

In the traditional methods developed in the 19th century and at the beginning of the 20th century, hydrolysis is performed by attacking the cellulose with an acid. Dilute acid may be used under high heat and high pressure, or more concentrated acid can be used at lower temperatures and atmospheric pressure. A decrystalized cellulosic mixture of acid, and sugars reacts with the prescence of water to complete individual sugar molecules (hydrolysis). The product from this hydrolysis is then neutralized and yeast fermentation is used to produce ethanol. A significant obstacle to the dilute acid process is that the hydrolysis is so harsh that toxic degradation products are produced which is a hurdle for fermentation. Concentrated acid must be separated from the sugar stream for recycle (simulated moving bed (SMB) chromatographic separation for example) to be commercially attractive.

[edit] Enzymatic Hydrolysis

Cellulose chains can be broken into glucose molecules by cellulase enzyme. This reaction occurs at body temperature in the stomach of ruminants such as cows and sheep, where the enzymes are produced by bacteria—there are actually at least three enzymes, used at various stages of this conversion.

If the enzymatic hydrolysis process takes place with previously isolated enzymes, a steady supply of the cellulase enzymes is needed.

Iogen Corporation is a Canadian producer of enzymes. They are promoting an enzymatic hydrolysis process that uses "specially engineered enzymes". The raw material (wood or straw) has to be pre-treated to make it amenable to hydrolysis.

Genencor and Novozymes 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 of cellulosic ethanol by enzymatic hydrolysis.

Other enzyme companies, such as Dyadic International, Inc. (AMEX: DIL), are developing genetically engineered fungi which would produce large volumes of cellulase, xylanase and hemicellulase enzymes which can be utilized to convert agricultural residues such as corn stover, distiller grains, wheat straw and sugar cane bagasse and energy crops such as switch grass into fermentable sugars which may be used to produce cellulosic ethanol.

There are four or five stages in this process:

A "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;
Yeast fermentation of the sugar solution;
Distillation to produce 99.5% pure alcohol.

Alternatively, instead of producing and recovering the enzymes to do the hydrolysis and fermentation separately, it is possible to use bacteria that does both (For more details on this topic, see Bioconversion of biomass to mixed alcohol fuels).

[edit] Gasification process

Fluidized Bed Gasifier in Güssing Burgenland Austria

The gasification process does not rely on chemical decomposition of the cellulose chain. Instead of breaking the cellulose into sugar molecules, the carbon in the raw material is converted into synthesis gas, using what amounts to partial combustion. The carbon monoxide, carbon dioxide and hydrogen may then be fed into a special kind of fermenter. Instead of yeast, which operates on sugar, this process uses a microorganism named “Clostridium ljungdahlii” ^[1]. This microorganism will ingest (eat) carbon monoxide, carbon dioxide and hydrogen and produce ethanol and water. The process can thus be broken into three steps:

Gasification — Complex carbon based molecules are broken apart to access the carbon as carbon monoxide, carbon dioxide and hydrogen are produced
Fermentation — Convert the carbon monoxide, carbon dioxide and hydrogen into ethanol using the Clostridium ljungdahlii organism
Distillation — Ethanol is separated from water

A recent study has found another Clostridium bacteria that seems to be twice as efficient in making ethanol from carbon monoxide as the one mentioned above^[2]

Alternatively, the synthesis gas from gasification may be fed to a catalytic reactor where the synthesis gas is used to produce ethanol and other higher alcohols as well^[3]

[edit] Economic importance and viability

The quest for alternative energies has provided many ways to produce electricity, such as wind farms, hydropower, or solar cells. However, about 40% of total energy consumption is dedicated to transportation (ie cars, planes, lorries/trucks etc) and currently requires energy-dense 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.^{[citation needed]}

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. When produced from wood products it is referred to as treethanol.^{[citation needed]}

The raw material is plentiful. Cellulose is present in every plant: straw, grass, wood. Most of these "bio-mass" products are currently discarded^{[citation needed]}. Transforming them into ethanol using efficient and cost effective hemi(cellulase) enzymes or other processes 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.

In June 2006, a U.S. Senate hearing was told that the current cost of producing cellulosic ethanol is US $2.25 per US gallon (US $0.59/litre). This is primarily due to the current poor conversion efficiency.^[4] At that price it is not competitive when distribution costs are added. However, the Department of Energy is optimistic and has requested a doubling of research funding. The same Senate hearing was told that the research target was to reduce the cost of production to US $1.07 per US gallon (US $0.28/litre) by 2012.