Partnerships, Future, and Emerging Technologies - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 403

support to develop the technologies to a commercially viable state, and both routes
have the potential to make a significant contribution to the world's supply of
transportation fuels.
Biochemical
A schematic of a representative biochemical conversion process for cellulosic
ethanol is shown in Fig. 19.2 .
The biochemical conversion process can essentially be categorized into two
main subcomponents: the liberation of the sugars from the biomass and the fer-
mentation of these sugars to ethanol. The efficient liberation of sugars from the
carbohydrate portion of the biomass “saccharification” is a significant challenge
given the recalcitrant nature of biomass [ 11 ]. Saccharification research has received
considerable attention over the past couple of decades with significant improve-
ments made in both the efficiency and the cost of the process [ 12 ].
Saccharification can essentially be either a chemical process where a concen-
tration acid process or multiple stages of dilute acid are utilized to liberate both the
hemicellulose and cellulose sugars [ 13 ] or a two-step approach involving a
pretreatment step and a enzymatic hydrolysis used to liberate some to most of the
hemicellulose sugars and condition the biomass to a state that is amenable for
enzymatic hydrolysis [ 14 ].
The US Department of Energy (DOE) evaluated the long-term potential [ 15 ]of
these two approaches and determined that the pretreatment/enzymatic hydrolysis
approach had the best potential for efficient conversion at low cost for wide-scale
applicability [ 16 ]. Although this is true at the macroscale, chemical saccharification
technologies such as concentrated acid or multistep dilute acid approaches are
certainly viable for special niche applications.
Fig. 19.2 Biochemical conversion process schematic