Biofuels - The Oxford Topic of Food, Politics, and Society - page 188

grassland into ethanol at the optimistic rate given by Tilman et al. would provide only
12% of annual consumption of US oil, and it of course assumes that there is food to burn
(USDA 2006; USCB 2008). Verified data, however, confirm that the output in ethanol
would require 1.5 liters of oil equivalents to produce 1 liter of ethanol (Pimentel et al. 2009).
The amount of electricity produced by the ethanol from 1 ha of switchgrass can be matched
by 30 square meters of 10% efficient (considered inefficient) photovoltaic cells, and pho-
tovoltaic cells are designed to run for 30 years with very little maintenance (Patzek 2012).
To achieve the production of this much ethanol, US farmers would have to displace
the 100 million cattle, 7 million sheep, and 4 million horses that are now grazing on
324 million ha of US grassland and rangeland (USDA 2006). Overgrazing is already a
serious problem on US grassland, and an overgrazing problem exists worldwide (Brown
2002). Thus, the assessment of the quantity of ethanol that can be produced on US and
world grasslands by Tilman et al. (2006) appears to be unduly optimistic.
Converting switchgrass into ethanol results in a negative energy return (Pimentel
et al., 2009). The negative energy return is 57%, or a slightly more negative energy return
than corn ethanol production (Pimentel et al. 2009). The cost of producing a liter of
ethanol using switchgrass was 93¢ in 2009 (Pimentel et al. 2009).
Several problems occur in the conversion of cellulosic biomass into ethanol. First,
from two to five times more cellulosic biomass is required to achieve the same quan-
tity of starches and sugars as are found in a given quantity of corn grain, since no ener-
getically efficient or economically viable method exists to break the cellulose down
into simple sugars (Pimentel et al. 2012). Thus, two to five times more cellulosic mate-
rial must be produced and handled, compared with corn grain (Pimentel and Patzek
2007). In addition, the starches and sugars in cellulosic biomass are tightly held in lig-
nin. These starches and sugars can be released using a strong acid to dissolve the lignin.
Once the lignin is dissolved, the acid action is stopped with an alkali. The solution of
lignin, starches, and sugars can be fermented. Some claim that the lignin can be used as
a fuel, but not when dissolved in water. The lignin in the water mixture can be extracted
using various energy-intensive technologies. Usually less than 25% of the lignin can be
extracted from the water mixture (Pimentel and Patzek 2007).
Soybean Biodiesel
Processed vegetable oils from soybean, sunflower, rapeseed, oil palm, and other oil
plants can be used as fuel in diesel engines. Unfortunately, producing vegetable oils for
use in diesel engines is costly in terms of economics and energy. Comparative analysis
concludes that these sources should be exploited only in situations where accumula-
tions of waste or by-product vegetable oil already exist (Ozaktas 2000; Pimentel and
Patzek 2007; Pimentel et al. 2009). A slight net return on energy from soybean oil is
possible only if the soybeans are grown without commercial nitrogen fertilizer. Under
favorable conditions, the soybean, a legume, will produce its own nitrogen. Still, soy