and reported 2% w/v NaOH concentration, 15% w/v biomass loading, autoclaved at
121
C for 15 min, followed by 2% w/v sulfuric acid concentration autoclaved at
121
C for 15 min with 15 lb./in
2 . Raghavi et al. [16] developed a novel sequential
pretreatment for the bioethanol production from sugarcane trash. Authors observed
2.3% lignin and 47.5% hemicellulose removal under the optimal conditions of 3%
v/v glycerol in presence of 1% NaOH and different transition metal concentration of
1% w/w at 121
C for 60 min. Althuri and Banerjee [17] observed 70–80% lignin
removal by performing enzymatic pretreatment on SCT using 500 IU/mL laccase
maintained at pH 7 with substrate concentration of 30% (w/v) incubated at 35
C for
6 h.
4 Dilute Acid Pretreatment
Pretreatment of the biomass that acts as feedstock is the first step in the production of
bioethanol. It helps to alter the structure of the biomass and the chemical composition so that higher yields of monomeric sugars are obtained from the hydrolysis
process. The dilute acid pretreatment helps to disrupt the recalcitrant lignin structures
in the feedstock such as the covalent bonds present in it which helps further in the
hydrolysis process due to more accessibility of the enzymes. It solubilizes the
hemicellulose present in the biomass as well as makes the cellulose more accessible
[18, 19]. The xylan and glucomannan are relatively acid stable and hence will not be
affected during the acid pretreatment. The hydrolyzation of cellulose and the solubilization of the glucose result in an increase in the crystallinity index (CrI) in the
biomass which can be obtained from the XRD spectra [13].The type of pretreatment
employed and the process parameters plays an important role for the basis of lignin
removal. Dilute acid pretreatments are widely chosen for the pretreatment by the
industries due to its cost and its corrosion properties. The pretreatment efficiency
depends on several process parameters such as incubation temperature, biomass
loading, and the acid concentration. All these parameters in combination play an
important role to give better yield, and hence the optimization of the parameters is
considered to be necessary in order to produce high yield of monomeric sugars.
Pretreatment of SCT with sulfuric acid with mixed size particle and incubation
time of 60 min gave higher reducing sugar and improved the hydrolysis efficiency
fourfold when compared to the yield given by the native SCT. 3% w/w was found to
be more suitable in maximum reducing sugar production of 0.611 g/g. The effect of
biomass loading on acid pretreatment showed that 15% w/w is the optimum condition and the efficiency decreased with the further increase in the biomass loading
which could be due to decrease in the accessibility of the pretreatment agent [8].
The hybrid pretreatment involving surfactant and dilute acid has improved the
dissolution and hence the removal efficiency of lignin. It helps in the removal of both
hemicellulose and lignin. Triton X-100 as the surfactant in the presence of dilute
sulfuric acid was found to be more efficient in producing reducing sugar. The total
lignin content was reduced to 50% during the pretreatment process with the increase
94
S. Niju and M. Swathika
121
C for 15 min, followed by 2% w/v sulfuric acid concentration autoclaved at
121
C for 15 min with 15 lb./in
2 . Raghavi et al. [16] developed a novel sequential
pretreatment for the bioethanol production from sugarcane trash. Authors observed
2.3% lignin and 47.5% hemicellulose removal under the optimal conditions of 3%
v/v glycerol in presence of 1% NaOH and different transition metal concentration of
1% w/w at 121
C for 60 min. Althuri and Banerjee [17] observed 70–80% lignin
removal by performing enzymatic pretreatment on SCT using 500 IU/mL laccase
maintained at pH 7 with substrate concentration of 30% (w/v) incubated at 35
C for
6 h.
4 Dilute Acid Pretreatment
Pretreatment of the biomass that acts as feedstock is the first step in the production of
bioethanol. It helps to alter the structure of the biomass and the chemical composition so that higher yields of monomeric sugars are obtained from the hydrolysis
process. The dilute acid pretreatment helps to disrupt the recalcitrant lignin structures
in the feedstock such as the covalent bonds present in it which helps further in the
hydrolysis process due to more accessibility of the enzymes. It solubilizes the
hemicellulose present in the biomass as well as makes the cellulose more accessible
[18, 19]. The xylan and glucomannan are relatively acid stable and hence will not be
affected during the acid pretreatment. The hydrolyzation of cellulose and the solubilization of the glucose result in an increase in the crystallinity index (CrI) in the
biomass which can be obtained from the XRD spectra [13].The type of pretreatment
employed and the process parameters plays an important role for the basis of lignin
removal. Dilute acid pretreatments are widely chosen for the pretreatment by the
industries due to its cost and its corrosion properties. The pretreatment efficiency
depends on several process parameters such as incubation temperature, biomass
loading, and the acid concentration. All these parameters in combination play an
important role to give better yield, and hence the optimization of the parameters is
considered to be necessary in order to produce high yield of monomeric sugars.
Pretreatment of SCT with sulfuric acid with mixed size particle and incubation
time of 60 min gave higher reducing sugar and improved the hydrolysis efficiency
fourfold when compared to the yield given by the native SCT. 3% w/w was found to
be more suitable in maximum reducing sugar production of 0.611 g/g. The effect of
biomass loading on acid pretreatment showed that 15% w/w is the optimum condition and the efficiency decreased with the further increase in the biomass loading
which could be due to decrease in the accessibility of the pretreatment agent [8].
The hybrid pretreatment involving surfactant and dilute acid has improved the
dissolution and hence the removal efficiency of lignin. It helps in the removal of both
hemicellulose and lignin. Triton X-100 as the surfactant in the presence of dilute
sulfuric acid was found to be more efficient in producing reducing sugar. The total
lignin content was reduced to 50% during the pretreatment process with the increase
94
S. Niju and M. Swathika