Enzymatic Breakdown

We will begin by an overview of enzymatic breakdown. First let's try to define the overall technological problem of this pathway. Cellulose is a complex carbohydrate with hundreds of long molecular chains bound to each other. The cellulose is present in many agricultural materials. i.e. corn stover, wheat and rice straw, dedicated energy crops, wood and wood residues among others. The process of converting the cellulosic material to ethanol involves two key phases. The first phase is to break the long chains of cellulose molecules into glucose and other sugars. The second phase is to ferment these sugars into ethanol. These processes as they occur in nature are performed by different organisms: fungi and bacteria that use enzymes to free the sugar in cellulose; and other organisms, like yeasts, that ferment the sugars into ethanol.

Thus far the main challenge in producing cellulosic ethanol has been improving the biological efficiency and the cost of breaking down the cellulose into sugars. The key is to find and/or develop microbes or enzymes that can reduce the number of steps in the conversion process. However, this is not the only challenge. Once the enzyme has been developed, and its production mastered, and the system optimized to handle different sugars and to tolerate maximum levels of ethanol, then the process will be ready for commercial implementation. The ideal organisms would do it all: break down cellulose like a bacterium, ferment sugar like yeast, tolerate high concentrations of ethanol, and dedicate most of its metabolic resources to produce just ethanol.

Significant progress has been made in improving this process recently. In October of 2004, two firms working independently but both with support from the National Renewable Energy Laboratory (NREL) developed a genetically modified organism that produce large amounts of cellulose enzymes that digest cellulose efficiently. These companies were Novozymes a Denmark based company and Genecor a firm based in California. This development marked a milestone, because these enzymes were able to reduce the cost cellulose-digesting enzymes from 5 dollars per gallon in 2001 to 10-18 cents per gallon of ethanol; reducing the gap between the total cost of cellulosic ethanol and that of corn grain ethanol to 50 cents per gallons, given comparable cost of feedstock.

To keep improving the economic efficiency of the process, the new enzymes have to be integrated with more efficient pretreatment and fermentation steps. The purpose of the pre-treatment is to remove the complex hemicellulose and lignin compounds that surround plant material as a protective sheath around the cellulose. In this way the cellulose becomes more accessible to the enzymes that convert it into glucose. The improvements on the fermentation need to increase the ethanol concentration resulting from it. Abengoa Bioenergy an ethanol producer based in Spain will test Novozymes's process at a 0.53 million gallon capacity pilot plant in York, Nebraska.

In another front, a collaborative effort between Dartmouth University and University Stellenbosch in South Africa, lead by Dartmouth professor Lee Lynd, are working in collapsing the many biological intermediate steps in the production of ethanol into a single one. They have reported significant progress in developing a yeast that can survive on cellulose alone, breaking down the complex molecules and fermenting the resultant glucose into ethanol. The group has also developed a "thermophilic" bacterium (one that naturally lives in high-temperature environments, where commercial celluloses work best) whose only fermentation product is ethanol. This technologies are been marketed by Mascoma Corporation, a startup company in Cambridge Massachusetts. In fact, Mascoma Corporation and Tamarack Energy, Inc. of Essex

Connecticut, have agreed to collaborate on the joint development of cellulosic ethanol facilities in New York, and follow-up projects in Pennsylvania, and the New England states.

Synthetic Genomics, from Rockville Maryland, is in search for a bacterium that will do every thing. It is funding the work that scientist at the J. Craig Venter Institute to build new organisms that would produce ethanol and other biofuels.

Another significant event is the announcement by Xethanol Corporation of NewYork to build a 50 million gallon/year cellulosic ethanol plant in Augusta Georgia. Xethanol will partner with PRAJ Technology an India based world leader in bio-ethanol technology. The plant would be designed to process multiple cellulosic feedstocks; however it would start with the process of residues from forestry operations.

BlueFire Ethanol, a California base company has announced its intentions to build 20 cellulosic to ethanol plants in the next 6 years, with total capacity of 1.5 billion gallons of ethanol per year. For this purpose it has signed a memorandum of understanding with MECS, Inc. as its leads engineering and procurement contractor. BlueFire Ethanol was established to deploy the Arkenol process for the conversion of wood residues, urban-waste, and agricultural residues into ethanol.

Dupont and Chevron have also announced independent joint ventures to advance the conversion of cellulosic ethanol into biofuels. Dupont and ethanol producer Broin announce plans to produce biofuels from corn stover. Broin is planning to convert one of its six corn-to-ethanol plants in Iowa into a biorefinery that will use both corn grain and corn stover. Chevron and NREL signed a five year agreement for research and development of new production technologies for converting biomass, such as forestry and agricultural waste, into ethanol.

Iogen Corporation from Ottawa, Canada is teaming up with Royal Dutch Shell and Goldman Sachs, to expand its Ottawa pilot plant experience into a larger commercial operation. The pilot experience indicates that a larger, commercial plant will be capable of producing cellulosic ethanol at a starting price of $1.35 a gallon. That would be competitive with current gasoline prices, although it is still more expensive than the ethanol from a modern corn-ethanol plant, which the Energy Department figures at about $1 a gallon.

Toronto, Ontario-based SunOpta Inc. has sold a continuous process system for the conversion of biomass-to-ethanol to Dedham, Mass.-based Celunol Corp. The patented pretreatment and hydrolysis technology will prep and convert sugar cane biogasse and possibly hard wood waste to ethanol at a plant in Jennings, Louisiana. Celunol/BC International has been conducting research and development in Jennings with a small-scale pilot cellulose conversion system at an existing facility where much of the necessary infrastructure is already in place. BC International was renamed Celunol less than four months ago, and with four new venture capitalists on board the company is financially well-backed. The list of investors includes Vinod Khosla, founder of Sun Microsystems, who has heavily endorsed cellulosic ethanol as key to the future of transport fuels in the United States.

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