Page 42 - Lignocellulosic Biomass to Liquid Biofuels

Pretreatment of lignocellulosic biomass for efficient enzymatic saccharification of cellulose 21

Table 2.1 Primary types and functions of mechanical comminution for physical
pretreatment of biomass.
Items Types Size reduction Description References

Chipping For harvesting and From logs to Usually used to [11]
preconditioning coarse sizes reduce the size of
(about raw lignocellulosic
10 50 mm) biomass for further
Chipping for size Can reduce processing
reduction size to
10 30 mm
Grinding Ball milling 0.2 2 mm Can well reduce [8,12]
and cellulose
milling crystallinity of
lignocellulose
(vibratory ball
milling)
Hammer milling Being suitable for dry [7,14]
Knife milling biomass
Vibro milling Being suitable for [7,14]
both dry and wet
biomass (ball and
vibro milling)
Colloid milling
Tow-roll milling
Wet-disk milling Can achieve higher [13]
enzymatic
hydrolysis yield
than hammer
milling (disk
milling)
Attrition milling

are more suitable, while ball and vibro milling are more widely used and
suitable for both dry and wet biomass [7,14].
Size reduction by milling also has been employed independently to
improve the biodegradability of biomass conversion to biogas, bioetha-
nol, and biohydrogen. When rice straw was subjected to disk and ball
milling, the yields of glucose and xylose by enzymatic hydrolysis reached
up to 89% (from 78%) and 54% (from 41%), respectively [15]. Glucose
and xylose yield increased to 40% and 32% by wet disk milling for pre-
treated sugarcane bagasse and rice straw, respectively [16]. An obvious
advantage of mechanical comminution for size reduction is that no inhi-
bitors are generated during the process. However, various inhibitors are
generated in chemical pretreatments, such as hydroxymethylfurfural