1.1 Lignocellulosic biomass as a renewable resource for energetic, chemicals and materials platform

Lignocellulosic biomass (LCB) is the most abundant renewable resource on Earth, comprising about 50% of world biomass. LCB is outside the human food chain and its energetic content exceeds many times world basic energy requirements. These features make it an important option as feedstock, as a relatively inexpensive raw-material, for bioethanol production, and for the development of other bioindustries, to face the international demand for biofuel market. In 2008 it was estimated that 200 x 109 tons of biomass were produced and only 3% were used in pulp and paper industries (Rutz et al. 2008; Sanchez et al. 2008; Zhang 2008).

The use of LCB as feedstock for bioethanol production results in significant reduction of gas emissions (Sanchez et al. 2008; Brehmer et al. 2009) and in economic profits increase due to low-cost raw-materials (Balat et al. 2008). LCB can be classified based on their origin: wood (softwoods and hardwoods) and shrubs, non-food agricultural crops (kenaf, reed, rapeseed, etc.) and residues (such as olive stones, wheat straw, corncobs, rise husk, sugarcane and winemaking residues, among others), and municipal solid wastes related to thinning, gardening, road maintenance, etc. (Demirbas 2005; Balat et al. 2008; Sanchez et al. 2008). Wastes from pulp and paper industries, as spent liquors, paper broke, fibres from primary sludge, waste newsprint and office paper or recycled paper sludge are another specific group of LCB to consider.

The conversion of LCB to fermentable monomeric sugars is much more difficult than the conversion of starch. Numerous studies on the development of large-scale production of

ethanol from LCB have been carried out around the world in the last years (Mussatto et al. 2004). The particular inherent structure of LCB is the main limiting factor of its conversion to ethanol. Besides cellulose, with a broad range of applications, lignin and hemicelluloses are also considered promising raw materials for the aforementioned purposes. The brief presentation of potential pathways of lignin and hemicelluloses is depicted in Fig. 1 and Fig. 2, respectively.