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[posting]23242834[/posting]Interessant ist ein Projekt der spanischen Abengoa mit der dänischen Novozymes..... Weitere Pilotproduktion (2 Mill. Liter) für Biomasse in York, Nebraska, USA ab November 2006. Dadurch Kostensenkungen für Ethanol aus Biomasse auf ca. 1,50 USD je Gallone Ethanol. Overcoming the hurdles to producing ethanol from cellulose Countries around the world have strong incentives to find alternatives to petroleum-based fuels, and ethanol is broadly considered a strong candidate. Although a growing number of analyses of producing the alcohol from corn show that the fuel yields only a marginal energy return at best, the situation may be very different for ethanol created from the cellulose found in all plant material. New developments in producing ethanol from cellulose portend that agricultural wastes—including the stems and branches of corn plants—and quick-growing plants such as switchgrass could be abundant, cheap sources of the fuel. U.S. National Renewable Energy Laboratory Researchers have made significant progress in developing methods for producing ethanol from agricultural wastes such as sugarcane bagasse (shown).Two recent papers, one in ES&T (2006, 40, 1744–1750) and one in Science (2006, 311, 506–508), highlight the environmental advantages of cellulosic ethanol created from the cellulose in fibrous materials-wood chips, switchgrass, and farm residues such as corn and sugarcane wastes. The papers show that this ethanol requires much less petroleum and produces lower levels of greenhouse gas emissions than gasoline does. So far, the main hurdles in producing cellulosic ethanol have been reducing the cost and improving the efficiency of hydrolyzing cellulose, which is a complex carbohydrate with hundreds of long molecular chains bound to each other, to yield sugars. These sugars are then fermented to give ethanol. A major breakthrough came in October 2004 when two companies, Denmark-based Novozymes and California-based Genencor, both of which were working independently with support from the National Renewable Energy Laboratory (NREL), created genetically modified organisms that produce large amounts of cellulase enzymes that digest cellulose efficiently. The breakthrough has reduced the cost of cellulose-digesting enzymes to 10–18¢/gal of ethanol. This is a dramatic drop from the enzymes’ $5/gal cost in 2001; that price made cellulose hydrolysis the most expensive component needed to produce ethanol from cellulosic biomass. The cheaper price tag should bring down the total cost of cellulosic ethanol to ~$1.50/gal, making it more competitive with the cost of ~$1/gal for starch-based ethanol, according to Joel Cherry, Novozymes’s project leader. The key to reducing the cost of producing these cellulose-digesting enzymes was to increase their effectiveness so that a smaller quantity would do the job. Researchers at the companies started with the fungus Trichoderma reesei, which produces a large amount of cellulase. They collected different types of cellulase from other fungi strains, some natural and some genetically altered. They also created new, genetically modified forms of the enzyme. From among these hundreds of enzymes, they found combinations that worked synergistically to convert much more cellulose into glucose than is possible with any of the enzymes alone, Cherry says. So far, the companies have conducted laboratory-scale tests of the new cellulase enzymes with cornstalks that the NREL researchers pretreated with dilute acids and washed with a mix of hot water, alkali, and ethanol. The main purpose of these pretreatments is to remove the complex hemicellulose and lignin compounds that plant material contains as a protective sheath around the cellulose, so that the cellulose becomes more accessible to the enzymes that convert it into glucose. Novozymes and Genencor plan to integrate their cellulose digestion process with two other important manufacturing steps needed to make cellulosic ethanol commercially-biomass pretreatment and sugar fermentation. Ethanol producer Abengoa Bioenergy will test Novozymes’s process at a 0.53-million-gal-capacity pilot plant in York, Neb., beginning in November. The plant can process 1 t of dry agricultural residue in 24 h, says Abengoa representative Quang Nguyen. “For corn stover feedstock, one can expect an average ethanol yield of about 80 gal/t of dry material,” he says. For cellulosic ethanol to be affordable, the new enzyme breakthrough must also be integrated with improved pretreatment and fermentation steps, says Jim McMillan, the NREL biochemical engineer who coordinated the project. The type of raw material used and its pretreatment play a key role in maximizing the conversion of cellulose into sugar, Cherry explains. So finding a pretreatment that works best with a certain enzyme mix will reduce the costs further. “If you take a log and mix it with enzymes, you won’t break down any cellulose,” he says. “If you cut that log and make sawdust, heat that sawdust with water and... add acid to the water... then treat it with enzymes, you can break down a substantial amount of cellulose.” U.S. National Renewable Energy Laboratory Scientists are also looking at the non-food parts of the corn plant, which are known as corn stover, as a source of cellulose for producing ethanol.According to McMillan, the biggest technical hurdle keeping cellulosic ethanol from becoming cost-competitive with petroleum-based fuels is the fermentation technology. Enzymes can break up hemicellulose, which is the second biggest part of biomass after cellulose, into a type of sugar called xylose. However, the yeasts currently in use only ferment glucose sugar. As a result, the ethanol concentration is half of what it could be. “With cellulosic ethanol, we’re making beer, and we need to be making wine in terms of concentration,” McMillan says. David Friedman, the research director of the clean vehicles program at the Union of Concerned Scientists, compares cellulosic ethanol to hydrogen-battery technology, in the sense that “it’s very promising, but there are a lot of breakthroughs needed.” If all the pieces needed to make it can fit together and work on a large scale, the result will be a cheap fuel that, compared with starch-based ethanol, would produce lower levels of greenhouse gas emissions and compete less with food sources. “It takes a toolbox, not a silver bullet, to end our oil addiction, and cellulosic ethanol can be one tool in the toolbox,” Friedman says. —PRACHI PATEL-PREDD http://pubs.acs.org/subscribe/journals/esthag/40/i13/html/07… |
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| aus der Diskussion: | Abengoa - Ethanol und Solarkraftwerke Teil. 2 |
| Autor (Datum des Eintrages): | bossi1 (30.07.06 23:18:05) |
| Beitrag: | 115 von 2,406 (ID:23244947) |
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