5.1 Introduction
Biofuels like bioethanol have been seen to gain the peak of attention as they may be
acting as the substitute to fuels that are based on petroleum, and may protect the
reserves of oil and also may reduce the greenhouse gases and atmospheric carbon
dioxide (Parawira and Tekere 2011; Sarawan et al. 2019). To some extent, it is used
for the replacement of a mixture of ethanol and gasoline, E85 (85% ethanol and 15%
gasoline) and E15 (15% ethanol and 85% gasoline). This fuel is a liquid based in
nature which can possibly be produced from many kinds of biomass and conversion
techniques (Vohra et al. 2014). The focus of research has been changed to non-food
biomass (Deshavath et al. 2017). In case of second generation of bioethanol production, the biomass type is lignocellulose, and it is rich in cellulose which is same
as sugar and starch as it is also a glucose polymer (Tran et al. 2019). Also,
lignocellulose consists of lignin and hemicellulose, lignin is not cellulosic in nature
so is not fermentable (Nguyen et al. 2018).
For making the cellulose available from lignocelluloses and increasing the rate of
fermentation, pretreatment is performed. But this pretreatment is associated with the
production of derived microbial inhibitors (Hou et al. 2019).
A large number of biomass feedstock overlapping the three generations, i.e., first,
second, and third, had been utilized for production of biofuel. The feedstocks
involved in the first generation are the ones that are rich in sucrose, e.g., sugar
beet, sweet sorghum, sugarcane, and fruits, and also involve the feedstocks rich in
starch, e.g., wheat, corn, potato, rice, barley, cassava, and sweet potato. The next
generation of biofuel is related to substances rich in lignocelluloses, e.g., straw,
grasses, and wood. The last generation of biofuel comes from biomass of algae, i.e.,
macroalgae and microalgae (Azhar et al. 2017; Soccol et al. 2019). The most
efficient method is the second-generation bioethanol production. The 2G feedstocks
are chemically composed of carbohydrates and lignin, e.g., minerals, ash, salts,
pectin, cellulose, and hemicelluloses (Ravindran and Jaiswal 2016). Polysaccharides
are present in lignocelluloses-rich materials, which are seen to be un-accessible for
further processings like bioconversion. For this problem, pretreatment has become
an important step in making the cellulose accessible to enzymes (Hou et al. 2019;
Kumar et al. 2019; Watanabe et al. 2019).
Lignocelluloses have many polymers in it, and the main polymers included are
lignin, cellulose, and hemicellulose (Alonso et al. 2012); they also contain some
other molecules in small amounts, e.g., minerals, acetyl groups, phenolic compounds, and some others are present in trace amounts (Agarwal et al. 2017). The
percentages of these molecules differ based on their origin. However, the generalized percentages of the components of lignocellulosic biomass are summarized in
Fig. 5.1 (Madadi et al. 2017a).
Cellulose and hemicellulose (carbohydrates) together make almost 70% of
LB. Their high percentage in LB is the main benefit of utilizing these in bioethanol
production (Cheng et al. 2008). Only these carbohydrate components are the basic
ones for the bioethanol (and other biochemical) production after fermentation.
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Biofuels like bioethanol have been seen to gain the peak of attention as they may be
acting as the substitute to fuels that are based on petroleum, and may protect the
reserves of oil and also may reduce the greenhouse gases and atmospheric carbon
dioxide (Parawira and Tekere 2011; Sarawan et al. 2019). To some extent, it is used
for the replacement of a mixture of ethanol and gasoline, E85 (85% ethanol and 15%
gasoline) and E15 (15% ethanol and 85% gasoline). This fuel is a liquid based in
nature which can possibly be produced from many kinds of biomass and conversion
techniques (Vohra et al. 2014). The focus of research has been changed to non-food
biomass (Deshavath et al. 2017). In case of second generation of bioethanol production, the biomass type is lignocellulose, and it is rich in cellulose which is same
as sugar and starch as it is also a glucose polymer (Tran et al. 2019). Also,
lignocellulose consists of lignin and hemicellulose, lignin is not cellulosic in nature
so is not fermentable (Nguyen et al. 2018).
For making the cellulose available from lignocelluloses and increasing the rate of
fermentation, pretreatment is performed. But this pretreatment is associated with the
production of derived microbial inhibitors (Hou et al. 2019).
A large number of biomass feedstock overlapping the three generations, i.e., first,
second, and third, had been utilized for production of biofuel. The feedstocks
involved in the first generation are the ones that are rich in sucrose, e.g., sugar
beet, sweet sorghum, sugarcane, and fruits, and also involve the feedstocks rich in
starch, e.g., wheat, corn, potato, rice, barley, cassava, and sweet potato. The next
generation of biofuel is related to substances rich in lignocelluloses, e.g., straw,
grasses, and wood. The last generation of biofuel comes from biomass of algae, i.e.,
macroalgae and microalgae (Azhar et al. 2017; Soccol et al. 2019). The most
efficient method is the second-generation bioethanol production. The 2G feedstocks
are chemically composed of carbohydrates and lignin, e.g., minerals, ash, salts,
pectin, cellulose, and hemicelluloses (Ravindran and Jaiswal 2016). Polysaccharides
are present in lignocelluloses-rich materials, which are seen to be un-accessible for
further processings like bioconversion. For this problem, pretreatment has become
an important step in making the cellulose accessible to enzymes (Hou et al. 2019;
Kumar et al. 2019; Watanabe et al. 2019).
Lignocelluloses have many polymers in it, and the main polymers included are
lignin, cellulose, and hemicellulose (Alonso et al. 2012); they also contain some
other molecules in small amounts, e.g., minerals, acetyl groups, phenolic compounds, and some others are present in trace amounts (Agarwal et al. 2017). The
percentages of these molecules differ based on their origin. However, the generalized percentages of the components of lignocellulosic biomass are summarized in
Fig. 5.1 (Madadi et al. 2017a).
Cellulose and hemicellulose (carbohydrates) together make almost 70% of
LB. Their high percentage in LB is the main benefit of utilizing these in bioethanol
production (Cheng et al. 2008). Only these carbohydrate components are the basic
ones for the bioethanol (and other biochemical) production after fermentation.
120
FaizaKausar et al.