Page 23 - Lignocellulosic Biomass to Liquid Biofuels

4 Lignocellulosic Biomass to Liquid Biofuels

the main structural constituent of the primary cell wall of green
plants, algae, and oomycetes.
Cellulose is the most common and available organic polymer material
in the world. Cotton fiber is containing 90% of cellulose content, wood is
40% 50%, and dried hemp is containing approximately 57%. Higher
amounts of cellulose are contained in wood pulp and cotton for the
industrial use. Cellulose is frequently used to yield paperboard and paper-
type materials. A prospective characteristic of cellulose is crystallinity.
Cellulose is transformed into amorphous solid when the reactor environ-
ment is controlled as 25 MPa pressure and the temperature of water as
320°C. Several environment-friendly biofuels can be derived from con-
version of cellulosic materials, such as agricultural residues and energy
crops.

1.2.2 Hemicellulose
Hemicellulose is a branched heteropolymer containing approximately
500 3000 sugar units [8]. It consists in different sugar units, with a preva-
lence of pentose components (xylose and arabinose) together with hexoses
(mannose, glucose, galactose, and rhamnose) and acetylated sugars.
Hemicellulose cross-links with either cellulose or lignin, strengthening the
cell wall (Fig. 1.1). Although hemicelluloses are widely available, their uti-
lization is more difficult in comparison to cellulose, due to its structural
diversity, and also because the enzymatic hydrolysis of pentose sugar units
is less simple. However, hemicelluloses offer more possibilities for regiose-
lective chemical and enzymatic modifications in comparison to cellulose,
due to the variability in sugar constituents, glycosidic linkages, and struc-
ture of glycosyl side chains as well as two reactive hydroxyl groups at the
xylose repeating unit. In this view a bog effort is being made in research
activity.

1.2.3 Lignin

Lignin is the third major component of LCB having polymeric complex
structure, which is responsible for some of structural materials in the par-
ticular types of tissues of vascular plants and some of algae [10].Itisan
inevitable part of plant cell wall, especially in bark and wood. Because of
cross-linked phenolic polymers in its structure, it shows rigidity and hard
quality. It is mainly amorphous (noncrystalline). Lignin is branched long-
chain polymer made up of three types of monomers, such as primarily