3.2 Biochemical Conversion Technologies
85
Fig. 3.7 Pre-treatment methods for the lignocellulosic or microalgal biomass prior to fermentation
monomers [98, 99]. The most important factor in the pre-treatment of lignocellulosic material is to decompose the polysaccharides effectively while suppressing
the formation of undesirable inhibitors such as furfural and 5-hydroxymethyl
furfural that are formed as the result of monosaccharides degradation [100]. The
fermentable sugars are then metabolized by microorganisms to generate bioethanol
through fermentation. Pre-treatment methods include hydrothermal, chemical, physical, biological, physiochemical and combined processes (Fig. 3.7) and are briefly
described below [98, 101].
3.2.3.1 Hydrothermal Pre-treatments
Hydrothermal pre-treatments are mild treatment methods in which water is used in
liquid or vapor phase mostly in subcritical or near-critical conditions [3, 33, 38].
This method is considered as a cost-effective and environmentally friendly treatment
because (1) no chemicals or catalysts are needed during the treatment, (2) it has less
equipment corrosion issues compared with chemical methods and (3) the operation is
simple and economical [102, 103]. Water at these conditions has a much higher ionic
product (K W =
H
+
OH
−
) than the water at ambient temperature and pressure.
This means that more H
+ and OH
− will be released in water, which promotes the
85
Fig. 3.7 Pre-treatment methods for the lignocellulosic or microalgal biomass prior to fermentation
monomers [98, 99]. The most important factor in the pre-treatment of lignocellulosic material is to decompose the polysaccharides effectively while suppressing
the formation of undesirable inhibitors such as furfural and 5-hydroxymethyl
furfural that are formed as the result of monosaccharides degradation [100]. The
fermentable sugars are then metabolized by microorganisms to generate bioethanol
through fermentation. Pre-treatment methods include hydrothermal, chemical, physical, biological, physiochemical and combined processes (Fig. 3.7) and are briefly
described below [98, 101].
3.2.3.1 Hydrothermal Pre-treatments
Hydrothermal pre-treatments are mild treatment methods in which water is used in
liquid or vapor phase mostly in subcritical or near-critical conditions [3, 33, 38].
This method is considered as a cost-effective and environmentally friendly treatment
because (1) no chemicals or catalysts are needed during the treatment, (2) it has less
equipment corrosion issues compared with chemical methods and (3) the operation is
simple and economical [102, 103]. Water at these conditions has a much higher ionic
product (K W =
H
+
OH
−
) than the water at ambient temperature and pressure.
This means that more H
+ and OH
− will be released in water, which promotes the