**3.2 Steam explosion**

Mason [36] first time introduced steam explosion in which biomass is pretreated at 180–240°C under 1–3.5 MPa pressure for 1–10 min with hot steam, followed by

**63**

**Figure 6.**

*A pressure wave traveling through a solution [36].*

*Overview of the Process of Enzymatic Transformation of Biomass*

an explosive decompression which bursts the rigid biomass fibers [37]. Nature of material to be processed and particle size are the determining factor for relationship between temperature and time [38]. Quick expansion in steam explosion vaporizes the saturated water present in fibril structure linkages between molecules, and produces a better lignocellulosic matrix [39]. Recoveries ranged from 46 to 90% indicated that significant autohydrolysis and degradation of sugars can occur during this pretreatment process [40]. Steam provides an effective mean to rapidly attain the required temperature without diluting the resulting sugar syrup. At the end, a rapid release of pressure brings temperature down and arrests the reaction [41].

Scanning electron microscopy images reveal that ultrasonic treatment have the capacity to modify structure of lignocellulosic biomass [42]. Ultrasonic waves work by creating pressure difference within a solution [43]. The pressure wave travels through the liquid medium creating alternate regions of high (compression) and

In this method lignocellulosic material is dipped in an acidic solution (typically H2SO4), and subjected to optimum temperature. Dilute sulfuric acid had been used at commercial scale for pretreatment of various biomasses such as Switch grass [44] Corn Stover [45] and Poplar [46]. By acid catalyzed hydrolysis (**Figure 7**) most of the hemicelluloses are almost removed from the micro fibrils of the biomass but delignification is achieved to a lesser extent. Dilute acids are highly effective in removing hemicelluloses as dissolved sugars as a result of which glucose yield from cellulose increase to almost 100%. The optimal conditions to attain maximum sugar

It is responsible for the saponification of inter molecule delignification of the hemicelluloses. The biomass is exposed for the enzymatic hydrolysis of cellulose and hemicelluloses. As compared to other methods of pretreatment, alkali pretreatment is carried out for longer duration at low temperature and pressure [39]. It is supposed to act by saponification of inter-molecular ester bonds which are found to present between hemicelluloses and other components [48] (**Figure 8**). It is mainly responsible for

*DOI: http://dx.doi.org/10.5772/intechopen.85036*

**3.3 Ultrasonic pretreatment**

**3.4 Acid pretreatment**

**3.5 Alkaline pretreatment**

low (rarefaction) pressure (**Figure 6**).

yield depends on the target to be achieved [47].

**Figure 5.** *Effect of pretreatment on lignocellulosic biomass [34].*

*Overview of the Process of Enzymatic Transformation of Biomass DOI: http://dx.doi.org/10.5772/intechopen.85036*

an explosive decompression which bursts the rigid biomass fibers [37]. Nature of material to be processed and particle size are the determining factor for relationship between temperature and time [38]. Quick expansion in steam explosion vaporizes the saturated water present in fibril structure linkages between molecules, and produces a better lignocellulosic matrix [39]. Recoveries ranged from 46 to 90% indicated that significant autohydrolysis and degradation of sugars can occur during this pretreatment process [40]. Steam provides an effective mean to rapidly attain the required temperature without diluting the resulting sugar syrup. At the end, a rapid release of pressure brings temperature down and arrests the reaction [41].
