Switchgrass Ethanol
Americans use 140 billion gallons of gasoline each year, but only 4.8 billion gallons is produced from ethanol and approximately 95% of ethanol is corn based
Maywa Montenegro gives the simple explanation of producing ethanol, “Creating ethanol involves leaching simple sugars from plant matter and fermenting them into alcohol, just like the process for making "corn liquor," or moonshine. It's affordable and effective.” Montenegro’s explanation sums up the process, but there is one significant difference between producing ethanol from corn and producing it from switchgrass. Montenegro explains that conventional ethanol is produced from simple sugars, and it is easiest to obtain these sugars from plants that concentrate sugars in certain parts. Corn is used widely because it concentrates these sugars in its kernels. The problem is that little of the plant is used in this method and a lot of biomass is not used (Montenegro). Switchgrass and biomass are actually converted into ethanol using same process. There is one extra step in ethanol production from switchgrass than from corn. C. Matthew Rendleman and Hosein Shapouri explain that switchgrass is composed of complex carbohydrates unlike the simple carbohydrates found in corn. The complexity of the carbohydrates in the switchgrass means that it must first be broken down into simple sugars before it can be fermented. To do this either sulfuric acid is added or enzymes are used. Glucose and other five and six carbon sugars are produced and are converted to ethanol by fermentation. In addition, there are also some non-glucose sugars produced, but they are not easily fermentable by Saccharomyces cerevisia, a naturally occurring yeast. This problem can be combated by genetically engineered yeasts, but the process is not economically viable (Rendleman 22).
Though the process of producing ethanol from switchgrass is still in its infancy, the benefits of switchgrass based ethanol are well known and agreed upon. The first big benefit is soil conservation. According to S.B. McLaughlin and M. E. Walsh, 2.7 million metric tons of soil organic matter (SOM) per year is lost in the United States. There is a large difference between erosion of cultivated row crops like corn and perennial grasses like switchgrass. Erosion of corn fields in Iowa was 70 times higher than perennial grass fields on similar land, and during heavy rains corn fields eroded up to 200 times more than the grasslands. Erosion of land washes away many chemicals used to increase production. The chemicals washed away not only harm the environment, but also the farmer’s pocket. It is estimated that $18 billion in fertilizer nutrients are lost to erosion annually in the U.S. Switchgrass not only retains more of the fertilizer, but it also uses less. Usually switchgrass only needs herbicides during the first year of what is usually a ten-year growth cycle (McLaughlin 320).
Using less fertilizer is only one of the energy saving benefits of switchgrass. McLaughlin and Walsh explain some of the others. Switchgrass has a higher energy output for a few reasons. The first is that the plant itself produces more energy. The biomass from switchgrass can be more easily converted into ethanol than the biomass from corn can; therefore, if one has equal amounts of corn and switchgrass, the switchgrass can produce more energy. It has been calculated that it takes 4.5 times more energy to produce an equivalent amount of ethanol from corn than it does from switchgrass. The differences in the way the plants are broken down, and the amount of energy produced when broken down accounts for the difference. When comparing switchgrass to corn one can see that switchgrass requires less energy for agricultural production, produces more energy in its biomass, and uses less energy to process the biomass into ethanol than corn does. All of the factors presented account for the fact that corn based ethanol has a 21% net energy gain while switchgrass based ethanol has a substantially higher 343% net energy gain (McLaughlin 321).
Some say that corn ethanol could be a "stepping stone" to cleaner fuels like cellulosic (from biomass) ethanol (Montenegro). New technologies for producing ethanol from biomass may make the technique more appealing than it currently is. Right now it takes an extra step to create ethanol from biomass which means more time and money than the technique used for corn based ethanol. Two new methods for producing ethanol form biomass are Countercurrent Hydrolysis and Enzymatic Hydrolysis, which was touched upon earlier. In Countercurrent Hydrolysis steam is first used to break down or hydrolyze most of the biomass and then acid is added to hydrolyze the rest. The idea is that the new method would reduce costs and increase glucose yields. In fact scientists have achieved glucose yields of over 90% in experiments using hardwoods. The second method, Enzymatic Hydrolysis, involves using a genetically engineered enzyme to break down the complex biomass. Studies are being done using enzymes in place of sulfuric acid, but the cost is too great to do this commercially. The goal is to engineer an enzyme that can both hydrolyze and ferment the biomass because the extra step of having to break down the biomass before fermentation is the biggest problem right now (Rendleman 23-24).
Works Cited
Brady, D., & Pratt, G. C. (2007). Volatile Organic Compound Emissions from Dry Mill Fuel. Journal of the
Air & Waste Management Association , 1091–1102.
McLaughlin, S. B., & Walsh, M. E. (1998). Evaluating Enviromental Consequences of Producing
Herbaceous Crops for Bioenergy. Biomass and Bioenergy , 317-324.
Montenegro, M. (2006, December 4). The Big Three :The numbers behind ethanol, cellulosic ethanol, and
biodiesel in the U.S. Retrieved November 25, 2007, from Grist:
http://grist.org/news/maindish/2006/12/04/montenegro/
Rendleman, C. M., & Shapouri, H. (2007). New Technologies in Ethanol Production. Washington D.C.:
United States Department of Agriculture.
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