Page 105 - Lignocellulosic Biomass to Liquid Biofuels

Bioconversion of lignocellulosic biomass to bioethanol and biobutanol 81

in 16 h. PEG prohibited the unproductive attachment of lignin to the sur-
face of the enzyme [173].
Pretreatment using microwave irradiation was found to boost the
enzymatic saccharification of rice straw by 31%. The enzymatic saccharifi-
cation was dependent on factors such as irradiation time, substrate concen-
tration, and microwave intensity [174]. Banerjee et al. [175] reported the
utility of the using liquid fraction obtained after alkaline peroxide-assisted
wet air oxidation (APAWAO) of rice husk during the process of enzy-
matic hydrolysis. The hydrolysis experiment was carried out with the
APAWAO pretreated solid fraction (in buffer) and slurry (solid fraction in
liquid fraction). It must be noted that the hydrolysis in the APAWAO
pretreated liquid fraction produced extra glucose when associated to
hydrolysis of the solid fraction in buffer medium. Thus recycling of
APAWAO liquid portion was feasible during enzymatic hydrolysis, which
caused in glucose production enhancement at 50°C hydrolysis tempera-
ture. The enzymatic cellulose conversion was up to 86 wt.% within 24 h,
and the glucose yield was 21 g glucose per 100 g of the untreated rice
husk. The effect of different dry matter loadings on the hydrolysis yield
was also investigated and has affected the conversion [175].
The structural distinctive of biomass affects the cellulose digestibility
with respect to the surface area of the particle, crystallinity of cellulose,
large pore volume, presence of lignin and degree of polymerization of
hemicelluloses, and acetyl group [176].
Ultrasound-assisted pretreatment is a promising and a novel process
which escalates the glucose yield after the enzymatic saccharification by
removing lignin and hemicelluloses [177].
Bian et al. [178] investigated the effect of ionic liquid ([Emim]Ac) pre-
treatment on the enzymatic hydrolysis of sugarcane bagasse sometime. It
has also been observed that ionic liquid pretreatment enhanced enzymatic
convertibility of cellulose and achieved 95.2% cellulose conversion after
96 h enzymatic hydrolysis. Lowering the degree of polymerization and
reducing cellulose crystallinity resulted in high hydrolysis convertibility
[178]. The enzymatic digestibility of cellulose was found to be more asso-
ciated with lignin removal than hemicelluloses solubilization [179].
The overall bioethanol production process economics can be improved
by operating hydrolysis of enzymatic at higher substrate concentration so
that the glucose yields in the hydrolyzate could be added. The substrate
concentration affects the rate and extent of the hydrolysis process. The
hydrolysis product and substrate concentration are inversely proportional
[180]. It is well acceptable that cellulolytic enzymes are completely