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N HIII <br />According to U.S. Department of Energy studies conducted by the Argonne <br />Laboratories of the University of Chicago, one of the benefits of cellulosic ethanol is <br />that it reduces greenhouse gas emissions (GHG) by 85 percent over reformulated <br />gasoline. By contrast, ethanol from corn, which most frequently uses natural gas to <br />provide energy for the process, may not reduce GHG emissions at all depending on <br />how the starch -based feedstock is produced. <br />There are five steps to produce ethanol using a biological approach: <br />1. A "pretreatment" phase to make the lignocellulosic material, such as wood, <br />straw or solid waste, amenable to hydrolysis, and to remove as many <br />contaminants as possible; <br />2. Cellulose hydrolysis (cellulolysis) to break down the molecules into sugars; <br />3. Separation of the sugar solution from the residual materials, notably lignin; <br />4. Microbial fermentation of the sugar solution; <br />5. Distillation to produce 99.5 percent pure alcohol. <br />The process is shown graphically in Figure B -12; however, steps 2, 3 and 4 are <br />shown in one stage or process. Abengoa accomplishes these steps in a single <br />reactor. <br />I. Pretreatment <br />The first stage is physical processing of the feedstock: size reduction and removal of <br />contaminants. This is similar to the production of RDF. This is especially important <br />with solid waste where the fermentable portion may only be 60 to 70 percent of the <br />feed. Once the MSW is physically prepared cellulose, its susceptibility to <br />fermentation is still curtailed by its rigid structure. As the result, an effective <br />additional treatment is needed to liberate the cellulose from the lignin seal and its <br />crystalline structure so as to render it accessible for a subsequent hydrolysis step. A <br />number of pretreatment approaches have been developed to liberate the cellulose <br />and increase its reactability. To date, the available pretreatment techniques include <br />acid hydrolysis, steam explosion, ammonia fiber expansion, alkaline wet oxidation <br />and ozone pretreatment. Besides effective cellulose liberation, an ideal pretreatment <br />has to minimize the formation of degradation products because of their inhibitory <br />effects on subsequent hydrolysis and fermentation processes. <br />GBB/C08027 -01 B -15 August 15, 2008 <br />