Wood is essentially composed of cellulose, hemicelluloses, lignin, and extractives. Table 7.1 presents major chemical compositions of some wood species.

7.2 The Biological Approach for Biomass Hydrolysis into Sugars

The biological approach for hydrolysis of biomass is composed of a pretreatment phase, to make the lignocellulosic material such as wood open to hydrolysis, fol­lowed by cellulose and hemicelluloses enzymatic hydrolysis to break them down into sugars; finally, separation of the sugar solution from the residual materials, mostly lignin and also some enzymes adsorbed on the lignin [3].

Fig. 7.1 Main structure of galactoglucomannans in softwood hemicellulose (R = CH3CO or H)

In addition to this, yields of enzymatic hydrolysis are ca. 80-85 %, the obtained sugar concentration in the medium is low as <12.5 %, and the energy costs for both pretreatment and excess water removal is relatively high, and ca. 20 % of the sugar product is required to make the processing enzymes. Also there is no past experience with such process at industrial scale.

Due to all the above-mentioned withdrawals in using a biological process, which might be the technology of choice in other cases, the use of chemical process seems
to be an optimal route for hydrolysis of biomass into sugars. This approach is further presented in this chapter.