Due to the different structural properties of the biomass used in biofuel production processes, various pretreatment methods have been developed. They are generally classified as physical, chemical, physicochemical, and biological (Alvira et al.
2010; Zabed et al. 2019).
9.2.1 Physical Methods
Physical preprocessing methods can be summarized as chipping, grinding, milling,
sonication, microwave usage, and extrusion. The goal of these kinds of mechanical
force pretreatment methods is to increase the surface area-to-volume ratio of the
material and the degree of polymerization by reducing the particle size and crystallinity of the lignocellulosic feedstock. Also, the yield from biomass can be increased
in this way (Alvira et al. 2010; Mood et al. 2013).
According to some studies, the particle sizes of the raw material used can be
reduced to 10–30 mm by chipping and further to 0.2–2 mm by grinding or milling
(Sun and Cheng 2002; Abdullah et al. 2020).
The microwave method is an alternative to the conventional heating technique
and can help increase the effectiveness of enzymatic hydrolysis by disrupting the
lignocellulosic structure (Mood et al. 2013), is a widely used biomass pretreatment
method, requires little energy and short process period, and is advantageous in terms
of ease of application (Moodley and Kana 2017). This method transforms most of
the biomaterial that is applied to gaseous products consisting of H 2 , CH 4 , CO, and
CO 2 (Huang et al. 2016a).
Ultrasonic waves in the sonication process help to increase the hydrolysis of
enzymes by breaking down the hemicellulose and cellulose structures in the biomass
(Gabhane et al. 2014).
In the extrusion method, which is a thermophysical pretreatment method, materials are exposed to processes such as mixing, heating, and shearing, so that physical
and chemical changes occur while they are passing through the extruder (Alvira et al.
2010; Mood et al. 2013).
9.2.2 Chemical Methods
Chemical pretreatment techniques applied to biomass include acidic, alkaline, and
ionic liquids and oxidizing agents (Abdullah et al. 2020). Thanks to these applications, the lignin and hemicellulose structures in the structure of the lignocellulosic
material are resolved, thereby facilitating the access of the hydrolytic enzymes to
cellulose used in the process (Rajak and Banerjee 2016; Bhatia et al. 2017).
Acid hydrolysis is a pretreatment method that provides high sugar yield from
lignocellulosic material and is frequently used (ye Lee et al. 2013). In this method, it
facilitates the access of the enzymes to the cellulosic unit by providing the
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T. Karaytuğ et al.
2010; Zabed et al. 2019).
9.2.1 Physical Methods
Physical preprocessing methods can be summarized as chipping, grinding, milling,
sonication, microwave usage, and extrusion. The goal of these kinds of mechanical
force pretreatment methods is to increase the surface area-to-volume ratio of the
material and the degree of polymerization by reducing the particle size and crystallinity of the lignocellulosic feedstock. Also, the yield from biomass can be increased
in this way (Alvira et al. 2010; Mood et al. 2013).
According to some studies, the particle sizes of the raw material used can be
reduced to 10–30 mm by chipping and further to 0.2–2 mm by grinding or milling
(Sun and Cheng 2002; Abdullah et al. 2020).
The microwave method is an alternative to the conventional heating technique
and can help increase the effectiveness of enzymatic hydrolysis by disrupting the
lignocellulosic structure (Mood et al. 2013), is a widely used biomass pretreatment
method, requires little energy and short process period, and is advantageous in terms
of ease of application (Moodley and Kana 2017). This method transforms most of
the biomaterial that is applied to gaseous products consisting of H 2 , CH 4 , CO, and
CO 2 (Huang et al. 2016a).
Ultrasonic waves in the sonication process help to increase the hydrolysis of
enzymes by breaking down the hemicellulose and cellulose structures in the biomass
(Gabhane et al. 2014).
In the extrusion method, which is a thermophysical pretreatment method, materials are exposed to processes such as mixing, heating, and shearing, so that physical
and chemical changes occur while they are passing through the extruder (Alvira et al.
2010; Mood et al. 2013).
9.2.2 Chemical Methods
Chemical pretreatment techniques applied to biomass include acidic, alkaline, and
ionic liquids and oxidizing agents (Abdullah et al. 2020). Thanks to these applications, the lignin and hemicellulose structures in the structure of the lignocellulosic
material are resolved, thereby facilitating the access of the hydrolytic enzymes to
cellulose used in the process (Rajak and Banerjee 2016; Bhatia et al. 2017).
Acid hydrolysis is a pretreatment method that provides high sugar yield from
lignocellulosic material and is frequently used (ye Lee et al. 2013). In this method, it
facilitates the access of the enzymes to the cellulosic unit by providing the
262
T. Karaytuğ et al.