30.4 Value Added Products from Lignocellulose and Starchy Residues
463
(HMF), citric acid and lysine. Some of the organic acids such as acetic acid, butyric
acid, lactic acid, oxalic acid, itaconic acid, succinic acid, and propionic acid are the
value added products produced from the lignocellulose and starchy residues. Apart
from these valuable chemical compounds, this feedstock can also be used for pro-
ducing renewable fuels such as biogas, bioethanol, and biobutanol.
30.4.1
Feasibility of Biobutanol Production from Lignocellulose
and Starchy Residues
The butanol production cost depends on the price of feedstock and its availability.
An economic analysis reports that 70% of the butanol production cost is associated
with the naturally available feedstock [21]. In 1950 corn and molasses were used as
a substrate for butanol fermentation but these substrates being expensive brought
high competence with the food production leading to increased cost of crops and
food. This problem today is overcome by using inexpensive and sustainable sources
such as lignocellulosic residues.
Some of the lignocellulosic resources already investigated for biobutanol produc-
tion are listed in Table 30.2. Other than these feedstock some of the lignocellulose
waste generated from agricultural activities such as wheat straw, corn stalk, oil palm
biomass, rice straw, sugarcane bagasse and energy crops such as switch grass, phrag-
mites and king grass have also been tested for biobutanol production [5].
30.4.2
Pretreatment
Pretreatment of lignocellulose is required to expose the cellulose and hemicellulose
for hydrolysis to get fermentable sugars. This step is crucial as yield of butanol and
its economy depends on the success of this pretreatment step. Many efforts have
Table 30.2
ABE and butanol yield comparison from different substrates.
Hydrolysis method
Substrate
ABE (g/l)
Butanol
yield (g/g)a)
ABE
yield (g/g)b) References
H2SO4 (3.05%,
64.02 min, 121 ∘C)
LPG
Cocoa pod
5.27
0.19
0.30
[28]
H2SO4 (1%, 60 min,
121 ∘C)
Apple pomace
10.70
0.22
0.34
[29]
H2SO4 (1%, 15 min,
121 ∘C)
Rice straw
20.05
0.34
0.58
[30]
Enzyme hydrolysis
Oil palm biomass
6.44
0.11
0.19
[31]
Direct fermentation
Date fruit
14.5
0.48
0.63
[32]
H2SO4 (0.75%, 45 min,
121 ∘C)
Wheat bran
11.80
0.41
0.54
[33]
None
Paper sludge
18.00
0.14
0.30
[34]
a)
g of butanol/g of total sugar.
b)
g of ABE/g of total sugar.