Page 67 - Lignocellulosic Biomass to Liquid Biofuels

46 Lignocellulosic Biomass to Liquid Biofuels

Figure 2.6 Schematic diagram of different combined pretreatment of lignocellulosic
biomass.

for softwood but alkalis are usually expensive; and organosolv and cellu-
lose solvent based pretreatments are limited by the relatively high cost of
chemicals and energy consumption for solvent recovery [4]. Therefore,
combinations of different pretreatments, for example, physical physical,
physical chemical, chemical chemical, and biological chemical (shown
in Fig. 2.6), have been found to be efficiently performed with lower pre-
treatment severity, shorter grinding time, decrease in the formation of
inhibitors, enhanced enzymatic hydrolysis efficiency, and reduction of
energy consumption [4].

2.5.1 Physicochemical pretreatment
2.5.1.1 Steam explosion
SE has a long history for biomass pretreatment and pulping. During steam
explosion, biomass substrates are heated with high-pressure saturated steam
for a short time, from few seconds to several minutes, and then the pres-
sure is swiftly reduced. By this sudden release of pressure, there is an
explosive decompression happening to biomass. Although chemicals can
be used to promote SE pretreatment, the SE process without the addition
of any other external chemicals is termed autohydrolysis [22]. Residence
time, temperature (pretreatment pressure), particle size, and moisture con-
tent are the key parameters affecting SE pretreatment efficiency [4].
Pretreatment temperature and pressure for typical SE range from 160°C to
260°C and 0.69 to 4.83 MPa, respectively [175]. By SE pretreatment, the