Environmental Engineering Reference
In-Depth Information
needed to open up the tightly bound structures contained in biomass. These are
mainly entanglements of lignin with the carbohydrate content that is to be released
and further processed, enabling sugar conversions (fermentation [see Chapter 13]
and chemical conversion strategies [see Chapter 18]). Pretreatment is a key
step to ensure sufficient conversion in such processes, and it is aimed at the reali-
zation of the following effects (Aresta et al., 2012; Mosier et al., 2005; Sun and
Cheng, 2002):
Increase of the accessible surface area
Decrystallization of cellulose
Partial depolymerization of cellulose
Dissolution of hemicellulose and/or lignin
Modification of lignin structure
Basically, in biorefineries, one can divide pretreatment based on chemical conver-
sion into two distinct groups (Lersch, in (Aresta et al., 2012)):
1. Hydrolysis processes
that are accompanied with cellulose dissolution
)
2. Pulping processes in which lignin is extracted from the biomass
(
“
sugarification
”
An overview of such pretreatment
techniques is given in Chapter 13 (see
Table 13.7).
15.2.3 Hybrid Concepts
Figure 15.6 shows a block diagram of a biorefinery based on a sugar platform
(obtained via (bio)chemical processing) and a syngas platform (generated via thermo-
chemical gasification). The fractionation step is not needed in all possible hybrid
schemes; it is needed, however, when biochemical conversion is intended to be the
first step, as molecular structure opening is then required.
Final
products
(Bio-)
chemical,
thermo-
chemical
conversion
Solvent
fractionation
Primary
products
Biomass
Fractions
Upgrading
By-
products
FIGURE 15.6
Generic schematic sequence of hybrid techniques. Based on De Wild (2011).
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