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Science 2.1 Summary of findings on corn-based ethanols 2.1.1. Findings from Oliviera et al. In the first of the presented works, (Oliviera et al, 2005), a very detailed study was carried out which compared ethanol produced in Brazil to that in the U. S. The analysis included energy balances from corn-ethanol production as well as impacts on carbon dioxide emissions. While much of the data that was used in this article came from disparate and at times disagreeing sources, the authors used reasonable compromise estimates. The compromise estimates were adopted for items such as corn yield and energy input for ethanol processing, among others. A summary of the findings from this paper are presented in Table 1. The table shows two important sets of data. The first set deals with the production rate of corn ethanol using modern farming techniques and equipment. Included here is the ethanol yield (liters) per hectare. In addition, the present author has calculated the percentage of corn cropland which would be required if all U.S. transport fuel was produced by corn ethanol. The second portion of the table shows information related to the carbon dioxide emissions from farming, processing, and transporting corn-based ethanol. Account is made for the uptake of carbon dioxide into the soil, which remains after crop harvest. It is seen that nearly 4000 kg of carbon dioxide are emitted for each hectare. When this carbon dioxide emission rate is applied to the required cropland for complete conversion to cornbased ethanol, it is seen that more than 800 gigagrams of carbon dioxide would be emitted. If the emitted carbon dioxide of Table 1 is compared with the emissions which occur when only gasoline is used, it is found that use of corn-based ethanol results in a 44% reduction of greenhouse gases. For this calculation, it was estimated that each U.S. car releases, on average, 5,732 kg of carbon dioxide per year so that the accumulated emissions for the U.S amount to 1.46 x 1012 kg per year. Finally, using the data from Oliviera, it is seen that the net energy benefit of corn-based ethanol is 1.1, so that 10% more energy is harvested than is required for all stages of growing, production, and transportation of ethanol. The small net energy yield resulted in the determination that if petroleum fuels were to be completely displaced by ethanol, it would require 600% of the available corn cropland. Oliviera et al. concludes that the potential for corn-ethanol to displace large portions of petroleum-based gasoline is very limited by the small increase of energy and by the other secondary problems posed by corn agriculture, including soil erosion and groundwater usage. In fact, the authors conclude that if the entire U.S. automotive fleet were to be powered by E85 fuel, it would require all the available U.S. cropland by year 2012. This scenario is obviously not viable for fuel production. An alternative scenario is presented wherein other agricultural sources are used for ethanol production, such as biomass residual, logging waste, etc. This alternative approach is mentioned briefly in the work but the concept is not developed further. Fushcia-Ann Hoover Replacements for Petroleum-Based Fuels 2.1.2. Findings from Hill et al. The next presented analysis is taken from a 2006 publication from the Proceedings of the National Academy of Sciences (Hill et al., 2006) which also provides detailed information regarding both the harvested outputs and required inputs to produce corn-based ethanol using currently available farming practices and technologies. The paper compares corn ethanol to biodiesel created from soybeans. In brief, the findings indicate that the net energy yield for corn-based ethanol is 6% and overall, greenhouse gas emissions from ethanol are 12% less than that which would occur if gasoline were the exclusive fuel. When credit was awarded to corn coproducts, the net energy benefit rose to 1.28 (28% more energy output than required for farming, production, and transportation). Similar to the findings of Oliviera, Hill’s results lead to the conclusion that if petroleum fuels were to be completely displaced by ethanol, it would require more farmland than is currently used for corn production (833%). Meanwhile, biodiesel created from soybeans resulted in a much higher net energy benefit (93%), however the energy yield was so small that there is no potential for soybean biodiesel to displace an appreciable amount of petroleum diesel. The marginal improvements which are available from corn-based ethanol led to the authors’ conclusion that corn-based ethanol provides a very small greenhouse gas reduction yet exposes the U.S. to other environmental and human health impacts from the various stages of farming and production. These negative impacts include the release of other airborne pollutants, water runoff, and pesticide use. It was the conclusion of the authors that corn ethanol and soybean diesel are not viable alternatives to petroleum fuels. They further promote the investigation of cellulosic ethanol, such as those discussed later in this report. They report that cellulosic ethanol production has the advantage of being grown on marginally productive land with very low energy inputs. The authors encourage the further study of cellulosic replacement of petroleum fuels. 2.1.3. Findings from Patzek A very complete and detailed analysis of the thermodynamics of the entire corn-ethanol cycle, which includes a discussion of the energy requirements and energy analysis, is presented in (Patzek, 2004). The author pays particular attention to farming techniques that are required to maintain the sustainability of cropland. For instance, the author evaluates all major fertilizers and even considers the age of manufacturing plants, which create various fertilizer ingredients. Patzek discusses the large variations in energy requirements with location. It was shown that corn farming in the states of Iowa and Indiana require much greater electricity inputs than does farming in Illinois and South Dakota. Other very detailed discussions are given to energy requirements for human labor, transportation, and machinery construction. The author’s detailed discussions are presented alongside a comparison of the then-available literature results to facilitate a critical analysis of the findings. In summary, Patzek concludes that corn-based ethanol production is not a viable solution for displacing petroleum-made fuels. His conclusion is based on a number of factors, primary among which is the negative energy yield rate. Among the key 24 University of St. Thomas McNair Research Journal
Science findings which can be distilled from the data in Patzek’s report, it can be shown that if corn-ethanol were used to completely replace all petroleum fuels, approximately 900% of the available corn cropland would be required. This large figure reinforces the other results that have been presented in the foregoing. Aside from the negative results with regard to the energy balance, shown in Table 3, Patzek also identifies other negative impacts of transitioning to corn ethanol. Among his findings are that the U.S. government heavily subsidizes corn-ethanol production yet corn-ethanol produces no net energy savings and no reduction in petroleum fuels. In addition, cornethanol refining has led to a number of localized environmental hazards including the emission of CO, NO, and other volatile compounds. Finally, and perhaps most important, is Patzek’s conclusion that conversion to corn-based ethanol will result in an increase of CO2 in the amount of 3100 kg per hectare. 2.1.4. Findings from Shapouri, et al. In 2002, Shapouri, et al. presented a study which investigated the energy balance of corn-based ethanol. One major focus of this report was the identification of differences in analyses which have led to varying conclusions regarding the potential of corn-based ethanol to displace petroleum-fuels. The conclusion drawn from this work is that corn ethanol yields a positive return on energy with a net energy yield ratio of 1.34 (34% more energy recovered than invested). The positive outcome of this analysis is partly due to the fact that the authors considered more efficient farming and refining technologies Another difference between this work and other publications is the method by which co-products are given energy credit. The authors clearly define four approaches used to award energy credits for co-product production. Then, one method was selected which is based on the replacement value of the co-product energy. A final distinction take from this paper is worthy of mention. That is, the authors investigated year-to-year crop yields and the effect of location on both yield and energy inputs. They then utilized 1996 data covering a nine-state region for their analysis. A summary of the energy balance taken from Shapouri, et al., is presented in Table 4. The farm inputs, expressed in Btu per bushel, have here been converted to Btu per gallon of ethanol. The energy yield of ethanol, 83,961 Btu/gal, exceeds the overall energy input of 77,238 Btu/gal. The difference between these values provides the net energy yield of 6723 Btu/gallon and an energy ratio of 1.08, as indicated in the table. When account is given 14,372 Btu/gal of co-product energy credits, the net energy yield increases to 21,100 Btu/gal and the energy ratio becomes 1.34. Among the reports discussed in this article, the results of Shapouri are among the most affirmative regarding the potential of corn-based ethanol as a sustainable and viable transportation fuel. Even using these data, it is estimated that 720% of farmed U.S. corn crop would be required to displace petroleum-derived fuels. University of St. Thomas McNair Research Journal Fushcia-Ann Hoover Replacements for Petroleum-Based Fuels 2.1.5. Findings from Pimentel et al. A series of reports has been produced by Pimentel (Pimentel, 1991; Pimentel, 2001; and Pimentel 2003) which provide an alternative assessment strategy from those presented in the foregoing. In general, the resulting analysis shows that corn-based ethanol yields less energy than required energy inputs, even when co-product credits are given consideration. It is relevant to consider the source of disagreement between Pimentel (and Patzek’s) analysis and those of the other researchers. Understanding the differences in the analysis is critical for setting a rational energy policy. It is also crucial for determining the impact on greenhouse gas reductions. In the following discussion, use will be made of the more recent work by Pimentel (2003), however the overall conclusions are in general agreement with his earlier work. One major difference among the sources is the presence or absence of energy requirements for the manufacture of farm machinery and the construction of buildings and refining plants. Pimentel included both costs in his analysis, whereas other researchers included neither. In addition, Pimentel’s work generally accounts for higher fertilizer application rates than other researchers. More importantly, Pimentel (and Patzek) calculate much higher energy requirements for processing corn to ethanol (approximately twice the requirement compared to Shapouri, 2001 and Wang, 1997). Another significant difference is that Pimentel accounted for distiller’s dried grain with solubles (DDGS) which is a dry-milling co-product. Other researchers, including Wang et al., 1997; and Shapouri et al., 2002 credited both wet- and dry-milling co-products in their analysis which led to a more positive support of ethanol. A summary of the data from Pimentel is shown in Table 5. It can be seen that, according to the analysis of Pimentel, corn-based ethanol is an energy-losing operation and is not a viable solution for reducing petroleum fuel consumption. 25
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