Biofuels in Perspective

50 Biofuels
gas benefit to the atmosphere, reducing greenhouse gas emissions by over 100 % versus
gasoline. 23–25
Scientists have tried for decades to overcome the recalcitrance of cellulose and to make
cellulosic ethanol commercially using high pressure, steam or strong acids to free cellulose
sugars. The federal government began investing in cellulosic ethanol in the 1970s, but
nearly three decades of research yielded only modest progress towards commercially
viable production. Because plants produce lignocellulose to provide structural integrity,
biomass has proven a challenging substrate.
In the late 1990s, scientists turned to a new technology for breaking down the lignocellulosic
structure. Industrial biotechnology, as this emerging field has come to be known,
makes use of the molecular machines that break down lignocellulose in nature, and improves
their effectiveness using an array of genetic tools originally developed to treat
diseases or improve crop varieties.
This biochemical approach makes use of cellulose-slicing proteins known as cellulase
enzymes, found in the intestines of termites or jungle-dwelling fungi, to isolate simple
sugars. The first big breakthrough in this technology came in 2005, when, under US DOE
contract administered by the National Renewable Energy Laboratory (NREL), enzyme
manufacturers Novozymes and Genencor announced that they had dramatically reduced
the cost of biochemical production of cellulosic ethanol. Until the companies’ announcements,
cellulase enzyme costs were generally acknowledged to be over $5.00 per gallon of
ethanol, making commercial biochemical production of cellulosic ethanol in a market of
$2.00 per gallon gasoline impossible. By 2005, both companies had developed genetically
enhanced microbes capable of producing cellulase enzymes for less than 20 cents a gallon.
Commercial production of cellulosic ethanol was within reach (see Figure 3.5).
Several technological challenges to commercial cellulosic ethanol production remain.
Current estimates of cellulosic ethanol production costs range from under $2.00 a gallon to
Figure 3.5 Biochemical production of cellulosic ethanol.
Source: Biotechnology Industry Organization.