Biomedical Engineering Reference
In-Depth Information
Table 4.3
Comparisons of ethanol extraction of wheat straw and
steam-exploded wheat straw (extracted by 50 % ethanol at 180
ı
C
for 1 h with a solid-to-liquid ratio of 1:50) [
47
]
Steam-exploded
wheat straw
Wheat straw
Yield of sugar (%)
0:00
25:22
Yield of sugar by enzymatic
hydrolysis (%)
21:87
30:33
Total yield of sugar (%)
21:87
55:55
Sugar content of recovered
lignin (%)
42:00
1:12
Delignification (%)
64:11
80:22
and is not feasible in actual production. Hydrogen peroxide has a strong ability for
oxidation delignification and more obviously under alkaline conditions. Chen and
Xu [
45
] invented a method of coupling steam explosion with alkaline hydrogen
peroxide oxidation to pretreat straw. Steam-exploded straw and alkaline hydrogen
peroxide solution were mixed in accordance with a weight ratio of 1:20-1:40 and
oxidized for 12-36 h. After the treatment, the sugar concentration in the hydrolysate
of steam-exploded straw increased to 100 g
L
1
[
46
].
4.4.2.2
Combination of Steam Explosion and Ethanol Extraction
In the steam explosion process, the hemicellulose can be effectively recovered.
Under the same processing conditions, lignin in the steam-exploded wheat straw
can be effectively isolated by ethanol extraction, and the recovered sugar yield
is 2.5 times that of direct ethanol extracted from wheat straw. Meanwhile, pure
xylose, glucose, and ethanol-extracted lignin can be obtained. The delignification
effect of wheat straw treated by steam explosion pretreatment and ethanol extraction
was higher than for the wheat straw treated by direct ethanol extraction. In the
process of steam explosion, lignin has been softened and partially fractured, making
the lignin easier to extract. The results of electron microscopy showed that, after
ethanol extraction, fiber cells of the ethanol extract of steam-exploded wheat straw
are dispersed, increasing the accessibility of cellulose and improving the perfor-
mance of enzymatic hydrolysis and fermentation of raw materials. Comparisons of
ethanol extraction from wheat straw and steam-exploded wheat straw are shown in
Table
4.3
.
4.4.2.3
Combination of Steam Explosion and Ionic Liquid Dissolution
Compared with traditional organic solvents and electrolytes, ionic liquids have
advantages in that they are colorless and odorless, produce less pollution, and
have stable chemical properties. The design of the ions can adjust the solubility
