Page 254 - Refining Biomass Residues for Sustainable Energy and Bioproducts

224 Refining Biomass Residues for Sustainable Energy and Bioproducts

(160 C 270 C) at pressure range of 20 50 bar for few seconds or minutes
(Kumari and Singh, 2018). Zhang et al. revealed that the steam-exploited sorghum
biomass exhibited enzymatic conversion efficiency of 70%. Glucose concentration
was found to be 25 g/L as compared to that of ionic liquid, lime, and dilute acid
pretreatment (Zhang et al., 2011). Sipos et al. (2009) impregnated sulfur dioxide
(SO 2 ) into sorghum bagasse and steam pretreatment was carried out to yield maxi-
mum cellulose conversion of 89% and 92% at 190 C for 10 min and 200 C for

5 min, respectively. However, Shen et al. (2011) obtained 153 g ethanol/kg sweet
sorghum bagasse and 72.7% ethanol conversion using steam-pretreated conditions
at 200 C for 7.5 min and 2.5% SO 2 impregnation. Damay et al. (2018b) yielded

maximum total sugars 37.3 wt.% by impregnating water in sweet sorghum stem and
steam explosion at 215 C for 2 min. Damay et al. (2018a) also found that when

sweet sorghum biomass impregnated with water produced first-generation sugars
and the solid residues was subjected to steam explosion to produce second-
generation sugars, and fermentation of these mixed sugars resulted maximum etha-
nol conversion of 90% and less inhibitor in broth compared to second-generation
sugar broth. While Pengilly et al. (2015) used optimum combination of enzyme
cocktails, that is, cellulase and endo-xylanse, to hydrolyze, the steam pretreated
sweet sorghum bagasse and yielded 364.8 g sugar/kg bagasse, which resulted 20%
more sugars than the SpezymeCP cellulase. Freezing is also a newly developed pre-
treatment method, where freezing thawing process of bulk biomass is done. In this
method the crystal formation generates the breaking force, which leads to the
destruction of lignocellulose (Kumari and Singh, 2018). In extrusion, lignocellulosic
biomass is exploited for shearing, mixing, and heating. This pretreatment leads to
reduction in particle size and higher degree of depolymerization is observed after
the pretreatment (Shirkavand et al., 2016).

10.3.2 Chemical
A solvent or chemical is applied to disrupt the components of biomass. The destruc-
tion of the lignocellulosic components is highly efficient among all methods. Still,
it has numerous disadvantages, such as the generation of toxic chemicals, carbohy-
drate loss, and high process cost. Alkali, acid, organic solvent, and ionic liquid are
the main constituents of chemical pretreatment (Rabemanolontsoa and Saka, 2016).
Alkaline pretreatment is efficient in eliminating lignin and additionally, it causes
the swelling of cellulose and hemicellulose, which partially degrades the crystals of
cellulose. Low-temperature alkali pretreatment of sorghum bagasse efficiently
improved the enzymatic hydrolysis and enhanced the ethanol production (Wu et al.,
2011). Similarly, researchers have been utilizing NaOH (0.5% 5%) for the pre-
treatment of sorghum bagasse, stalk, or biomass to enhance the enzymatic sacchari-
fication as well as subsequent ethanol production (Cao et al., 2012; McIntosh and
Vancov, 2010; Umagiliyage et al., 2015). Cao et al. (2012) observed dilute alkali
(NaOH) treatment with hydrogen peroxide treatment of sweet sorghum bagasse