[Carpenter Prairie Discussion] Fw: cellulosics 101

Tue Dec 29 11:02:15 CST 2009

FYI: A basic 101 course in "What is Cellulosics?" And should the conservation community engage into this important movement?         

Cellulosic Ethanol Feedstocks
Plants contain the cellulosic materials cellulose and hemicellulose. These complex polymers form the structure of plant stalks, leaves, trunks, branches, and husks. They are also in products made from plants, such as paper. Cellulosic feedstocks contain sugars within their cellulose and hemicellulose, but they are more difficult to biochemically convert into ethanol than starch- and sugar-based feedstocks. Cellulose resists being broken down into its component sugars. Hemicellulose is easier to break down, but the resulting sugars are difficult to ferment. The plant compound lignin also resists biochemical conversion.

Developing processes to break down these components of biomass economically has been the focus of research by the U.S. Department of Energy (DOE) and other government and industry groups. Significant progress has resulted in biochemical conversion processes to break down cellulose and hemicellulose and thermochemical conversion processes to break down lignin. Together, these processes could unlock the potential of cellulosic feedstocks for ethanol production. Visit the DOE Biomass Program's Deployment page to learn about DOE-supported cellulosic ethanol biorefinery projects and view a project map.

Cellulosic feedstocks suited to ethanol production include the following:

  a.. Agricultural residue-crop residues such as wheat straw and corn stalks, leaves, and husks 
  b.. Forestry residue-logging and mill residues such as wood chips, sawdust, and pulping liquor 
  c.. Grasses-hardy, fast-growing grasses such as switchgrass grown specifically for ethanol production 
  d.. Municipal and other wastes-plant-derived wastes such as household garbage, paper products, paper pulp, and food-processing waste 
  e.. Trees-fast-growing trees such as poplar and willow grown specifically for ethanol production 
These feedstocks have many advantages over starch- and sugar-based feedstocks. They are much more abundant and thus can be used to produce more substantial amounts of ethanol to meet U.S. fuel demand. They are waste products or, in the case of trees and grasses grown specifically for ethanol production, can be grown on marginal lands not suitable for other crops. Less fossil fuel energy is required to grow/collect them and convert them to ethanol (see Energy Balance of Ethanol), and they are not human food products.

However, limitations on cellulosic feedstock quantities do exist. For example, limits must be placed on the amount of crop residue removed to protect lands from erosion and to sustain soil organic carbon. The U.S. Department of Agriculture's Renewable Energy Assessment Project is determining the amount of residue needed to protect the soil resource, comparing economic implications of using stover as a bioenergy feedstock versus a source of carbon to build soil organic carbon, and providing harvest rate recommendations and guidelines.

To learn more, see the DOE Biomass Program's Bioethanol Feedstocks page.

Ethanol is used as a fuel in many countries, including Brazil, where it is produced from sugar cane and in the United States, where fuel grade ethanol is produced from corn. However, neither of these sources is cellulosic ethanol. Mascoma's transformative technology uses yeast and bacteria to produce ethanol from non-food agricultural and forestry materials sources such as switchgrass, wood, and agricultural waste. These sustainable raw materials are known as "feedstocks" or "cellulosic biomass".  

All plants convert solar energy into strongly linked chains of sugar known as cellulose. Anyone who has ever made beer knows that yeast can make ethanol from sugar. Yeast, however, cannot easily convert the sugar in cellulose to ethanol without the chains first being broken down into simple sugars. There are two principle approaches to breaking the cellulose chains into sugars. 

Thermochemical conversion involves the breaking down of biomass into a mixture of gases and then converting the gasses into ethanol. Although thermochemical conversional is a simpler and relatively mature technology, it requires significant capital and energy expenses.

Biochemical methods rely on the use of enzymes to break down the cellulose into sugar. Where do these enzymes come from? In Nature, organisms such as termites live on sugars derived from cellulose. Similar to humans, the digestive system of a termite requires bacteria to digest food. But in the case of termites, the resident bacteria produce special enzymes that can break down cellulose into simple sugars that are used to fuel the termite's body. In industry, the enzymes used to break down the cellulose into sugars come from yeast and bacteria which then also ferment the sugar into ethanol. 

No one knows the first use of ethanol (or alcohol) by humans but the discovery of stone-age beer containers suggests that the earliest fermentations were carried out about 12,000 years ago. From early production of wine and beer to fuel for Indy Race Cars, we are all familiar with ethanol. 

Ethanol's energy is derived from plants that in turn obtain their energy from the sun. In this way, ethanol acts as a means of storing solar power in liquid form. Cellulosic ethanol is ethanol that is obtained from the non-edible portion of plant material. Cellulosic ethanol is identical in composition and performance to ethanol derived from corn or sugar cane. Cellulosic ethanol, however, has important environmental, economic and sustainability advantages over conventional sources due to its source and method of production. 

 (From Mascoma Corporation web site)
In nature, there are few strains of yeast or bacteria capable of directly and efficiently producing ethanol from cellulosic biomass. The unique technology developed by Mascoma Corporation uses yeast and bacteria that are engineered to produce large quantities of the enzymes necessary to break down the cellulose and ferment the resulting sugars into ethanol. Combining these two steps (enzymatic digestion and fermentation) significantly reduces costs by eliminating the need for enzyme produced in a separate refinery. This process, called Consolidated Bioprocessing or "CBP", will ultimately enable the conversion of the solar energy contained in plants to ethanol in just a few days. This represents a vastly different time scale than the fossil fuels we use today which required millions of years to be formed from decomposing plants and animals.

Technological barriers to achieve CBP have been overcome by dedication and innovation. Mascoma Corporation recently announced major advances in CBP, which were heralded by biofuels expert Bruce Dale as "a true breakthrough that takes us much, much closer to billions of gallons of low-cost cellulosic biofuels. Many had thought that CBP was years or even decades away, but the future just arrived.

The Biomass Program uses the terms "Demonstration and Deployment" to describe on-the-ground activities, including biorefinery plant construction and operation. Engaging in actual fuel and co-product refining is a key segment of the Program's work toward increased biofuels production and use. In partnership with industry, deployment activities engage participants across a variety of available technologies and feedstocks, in the quest to develop clean, affordable, sustainable alternative fuels.

Information about the Biomass Program's complementary Research and Development activities, including detailed discussion of internal biorefinery and infrastructure efforts, can be found on this Web site's Technologies page.

Information about current funding opportunities for Demonstration and Deployment can be found on this Web site's Financial Opportunities page.

Map of DOE Cellulosic Biorefinery Deployment Projects (PDF 104 KB)

Integrated Cellulosic Biorefineries
On February 28, 2007, DOE selected six biorefinery projects to develop commercial-scale integrated biorefineries demonstrating the use of a wide variety of cellulosic feedstocks such as corn fiber, wood wastes, agriculture residues, municipal solid wastes and potential energy crops. The goal is to demonstrate that integrated biorefineries can operate profitably once their construction costs are covered and can be replicated. DOE will invest up to $385 million in the six projects over the next four years. When fully operational, these facilities will be capable of producing more than 130 million gallons of ethanol per year. 

While the refining process for cellulosic ethanol is more complex than that of corn-based ethanol, cellulosic ethanol yields a somewhat greater net energy benefit and results in lower greenhouse gas emissions. Of the six selected companies, four-BlueFire Ethanol, Inc., Poet, Iogen Biorefinery Partners, and Abengoa Bioenergy-will principally utilize biochemical processes to free the sugars from the biomass and then ferment them into alcohol. The two remaining companies, Range Fuels and Alico plan to use thermochemical processes to first gasify the biomass into a "synthesis gas." The synthesis gas will then be further converted to biofuels.

Current information about the projects and partner companies can be found on this Web site's Financial Opportunities page.

Ten Percent Validation - Small-Scale Cellulosic Biorefineries
On January 29, 2008, the Department of Energy (DOE) announced it will provide up to $114 million, over four years, to support the development of small-scale cellulosic biorefineries. The projects will develop biorefineries at 10% of commercial scale that produce liquid transportation fuels as well as biobased chemicals and bioproducts used in industrial applications. Projects selected to negotiate awards will use novel approaches and a variety of cellulosic feedstocks to test new conversion processes. Combined with industry cost share, more than $331 million will be invested in these four projects.

Current information about the projects and partner companies can be found on this Web site's Financial Opportunities page.

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