Lignocellulosic Materials: Sources and Processing Technologies

Abstract

Lignocellulosic biomass is a potential feedstock for the sustainable production of bioenergy and value-added products. However, the natural recalcitrance of this material is a major bottleneck for its exploitation. The current technologies require processing methods (i.e. pre-treatments) with severe conditions to disrupt the plant cell wall structure and remove their main components. So, pre-treatment is an important process in chemical and food engineering, enabling the recovery of valuable soluble components from raw materials. The processes should be energy-efficient, as simple as possible, cost-effective, environmentally friendly, applicable to a wide variety of feedstocks, and should ensure purity of the obtained products (Cybulska et al. 2013; Phitsuwan et al. 2013). Ongoing research is focusing on optimizing and improving these technologies in order to reduce the energy demands, the use of chemicals and the formation of by-products. 2.2 Lignocellulosic Materials: Definition, Composition and Sources Lignocellulose refers to the materials constituting the essential part of the cell wall of plants, i.e. cellulose, hemicellulose, and lignin (Fig. 2.1). Celluloses and hemi-celluloses (carbohydrates) are tightly linked to the lignin (aromatic polymer) through covalent and hydrogen bonds, making the structure highly complex and robust. Other components such as pectin, proteins, lipids, and ashes can also be found in these materials, but in less amount. The cellulose, hemicellulose, and lignin are mainly present in the secondary plant cell wall. In general, the plant cell wall is composed of distinct layers containing different components that vary considerably among them. The primary cell wall is normally very thin and the main