17.2 Processing of Lignocellulosic Biomass to Ethanol
269
Table 17.1
Summary of commonly used pretreatment methods with their advantages and
limitations.
Sl. No. Pretreatment
Nature
Intermediate
operation
Advantages
Disadvantages
References
1.
Mechanical
Physical
Temperature
greater than
300 ∘C with
sheer mixing
Amorphous and
crystalline
cellulose matrix
disruption
High energy
consumption
[1]
2.
Microwave
Physical
Microwave
irradiation
(optimized
according to
substrate)
Easy operation,
high heat
generation in
rapidly
High energy
consumption,
significant
when used with
alkali treatment
[2]
3.
Sonication
Physical
10–100 kHz
ultrasound
(power and
duration should
be optimized to
meet desired
pretreatment
effect)
Formation of
cavitation
bubbles that
ruptures cellulose
and
hemicelluloses
rapidly.
Sensitive
process.
Deviation in
power or
duration of
treatment can
adversely affect
the substrate
[3]
4.
Alkaline
Chemical
Sodium
hydroxide,
potassium
hydroxide,
ammonia
Lignin and
hemicellulose
degradation with
increased surface
accessibility
Frequent
washing
required, foul
odor and salt
formation
[4, 5]
5.
Acid
Chemical
Nitric acid,
sulfuric acid,
dicarboxylic
acid
Hemicellulose
solvation,
modifies lignin,
cellulose
swelling, and
inexpensive
Expensive,
hazardous and
corrosive,
production of
inhibitors
[6]
6.
Ozonolysis
Chemical
Ozone with low
moisture
biomass and
particle size
between 1 and
200 nm
Degrades lignin,
no toxin
inhibitors
production
Highly sensitive
and expensive
[7]
7.
Organosolv
Chemical
Aqueous
organic solvent
like alcohol,
ethylene glycol,
acetone with
specific
temperature
and pressure
Depolymerization
of lignin and
hemicellulose
Solvent
recycling and
draining
required,
formation of
inhibitors,
expensive
[8]
8.
Sulfite
pretreatment
to overcome
recalcitrance
of lignocellu-
lose
Physico-
chemical
Calcium or
magnesium
sulfite with disk
miller
Remove
hemicellulose,
dissolve, and
lignin sulfonation
Sugar
degradation,
large volume of
water required
post treatment
[9]
(Continued)