A great deal of hand-waving here and elsewhere is devoted to the potential of switchgrass ethanol as if it were an
industrial process on a
significant scale. This of course, is not a function of whether switchgrass ethanol is a
good idea: It may be a good idea or it might not, but it is
not immediately available.
That said, we need to determine through careful analysis, whether it is worth developing as a strategy for addressing climate change. A recent (2005) article in the scientific journal
Environmental Science and Technology helps provide such analysis by examining the position of switchgrass and corn stover derived cellulosic ethanol. (Environ. Sci. Technol. 2005, 39, 9750-9758)
Here are some relevant excerpts.
Fueling United States and Canada light-duty vehicles (LDV, cars and light trucks) with a domestically produced, cellulose derived fuel has the potential to be an attractive route toward improving environmental quality and sustainability of the countries’ energy and transportation sectors. The Province of Ontario is Canada’s largest provincial consumer of energy and highest greenhouse gas (GHG) emitter. In 2003, Ontario’s LDVs represented 37% of Canada’s total LDV fleet (1, 2), which in turn, was responsible for 25% of Canada’s total GHG Releases in 2001 (3). As a signatory to the Kyoto Protocol, Canada has pledged to reduce its GHG emissions by 6% below 1990 levels by 2008-2012. However, Canadian GHG emissions have actually risen by 20% since 1990, which means that very significant reductions are required under the Protocol (on the order of 155 Mt/year)...
...It is critical to differentiate cellulose-derived ethanol from the starch-derived ethanol currently produced in the United States/Canada primarily from corn (grain). Starch is a storage polymer consisting of a single sugar (glucose), which is relatively easy to hydrolyze, compared to cellulose, which is a structural polymer and more recalcitrant in nature. Starch-rich grains such as corn do not have the lignin energy source of cellulosic feedstocks such as corn stover, and thus existing starch-based ethanol cannot take advantage of additional energy savings...
...Uncertainties remain over the attractiveness of ethanol due to issues including biomass availability, net environmental impacts (7), economics, and scalability of new process technologies.A life cycle perspective is useful for determining the net environmental benefits/costs of cellulosic ethanol fueled vehicles compared to other fuel/vehicle alternatives...
...Life Cycle Inventory of Ethanol Production. Results for E100 (100% ethanol)-fueled vehicles (although the remainder of our analysis is limited to E85) are presented in Table 1 to illustrate the life cycle results associated solely with ethanol production and use, so as to distinguish these results from those when quantities of gasoline are blended with the ethanol. Table 1 shows the life cycle GHG emissions for E100 derived from switchgrass and corn stover divided among the three global warming gases (CO2,N2O, andCH4)...
From the perspective of global warming potential, with the assumptions employed in this study, ethanol from corn stover is slightly more attractive than that from switchgrass as reported in Table 1. The life cycle GHG emissions from corn stover-derived ethanol are 330 g of CO2 equiv/L compared to 489 g of CO2 equiv/L for switchgrass-derived ethanol (about 33% reduction). This result is primarily due to the lower demand for energy during crop production for corn stover due to the assumption of the one-pass collection system, which leads to allocating a portion of the collection
activities to the grain...
...The life cycle GHG emissions of the E85 vehicles are 57% and 65% lower than those of the RFG vehicle for switchgrass-and corn stover derived ethanol, respectively. The majority of the emissions in all cases are CO2. The emissions associated with the E85 vehicles are largely related to the production and combustion of the gasoline blend portion of the fuel, the application of fertilizer and herbicide during crop growth, and agricultural and transportation activities, which in the model assume the use of diesel fuel...
It is suggested in the article that, since some carbon dioxide is taken up during plant growth that overall the switchgrass ethanol is responsible for about 107 grams/liter produced of greenhouse gases, with a significant portion, more than 25%, coming from nitrous oxide emissions connected with fertilizer. Corn Stover ethanol gives about 87 grams of greenhouse gas per liter, with about half as much coming, in percentage terms, from nitrous oxide as compared to switch grass. The figure given for reformulated (petroleum based) gasoline is a whopping 252 grams, dominated of course by carbon dioxide.
This suggests that to the extent that it is available, switchgrass and corn stover derived ethanol can have a useful impact on climate change.
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