## 1 Introduction
### Chemical Composition of Lignocellulosic Biomass
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Lignocellulosic Substrates**} & \multicolumn{4}{c}{**Composition (\% Dry Basis)**} \\ \cline{2-5}  & **Cellulose** & **Hemicellulose** & **Lignin** & **References** \\ \hline Bamboo stem & 43.04 & 22.13 & 27.14 & [13] \\ Birch & \(40.1\pm 0.6\) & \(17.5\pm 0.2\) & \(24.2\pm 0.1\) & [14] \\ Corn cob & \(42.0\pm 0.1\) & \(45.9\pm 0.9\) & \(2.8\pm 0.2\) & [15] \\ Corn stalk & \(36.4\pm 0.1\) & \(30.3\pm 0.1\) & \(6.9\pm 1.4\) & [16] \\ Corn stover & \(42.21\) & \(22.28\) & \(19.54\) & [17] \\ Corn straw & \(49.3\pm 1.8\) & \(28.8\pm 1.4\) & \(7.5\pm 0.4\) & [18] \\ Cotton Stalk & \(41.6\pm 0.5\) & \(23.6\pm 0.4\) & \(23.3\pm 0.7\) & [19] \\ Eucalyptus & \(52.07\pm 2.6\) & \(24.51\pm 1.1\) & \(25.2\pm 1.1\) & [20] \\ Empty fruit bunch & \(34.9\) & \(26.64\) & \(31.1\) & [21] \\ Giant need & \(41.5\pm 2.6\) & \(20.5\pm 0.6\) & \(18.4\pm 1.4\) & [22] \\ Grass & \(47.12\pm 3.2\) & \(36.01\pm 3.17\) & \(11.55\pm 0.3\) & [23] \\ Maize straw & \(38.33\pm 0.8\) & \(29.76\pm 1.35\) & \(3.82\pm 0.5\) & [24] \\ Meadow grass & \(41.28\pm 5.3\) & \(28.14\pm 3.2\) & \(30.14\pm 7.9\) & [25] \\ _Miscanthus_ & \(36.3\pm 2.1\) & \(22.16\pm 1.9\) & \(22.55\pm 2.5\) & [26] \\ Olat straw & \(35.0\) & \(28.2\) & \(4.1\) & [27] \\ Oil palm empty fruit bunch & \(38.5\pm 1.9\) & \(26.1\pm 1.1\) & \(11.6\pm 1.6\) & [28] \\ Pinewood & \(38.2\pm 0.3\) & \(24.1\pm 0.7\) & \(34.4\pm 0.3\) & [29] \\ Poplar & \(46.0\pm 0.1\) & \(16.7\pm 0.1\) & \(26.6\pm 0.3\) & [14] \\ Rice hulls & \(36.0\) & \(12.0\) & \(26.0\) & [30] \\ Rice straw & \(37.8\pm 0.2\) & \(29.6\pm 0.7\) & \(14.8\pm 0.4\) & [31] \\ Rye Straw & \(36.5\pm 0.1\) & NR & \(21.3\pm 0.1\) & [32] \\ Sawdust waste & \(31.5\pm 1.3\) & \(26.1\pm 2.1\) & \(24.9\pm 1.7\) & [33] \\ Sorghum straw & \(26.93\pm 1.2\) & \(32.57\pm 1.9\) & \(10.16\pm 1.8\) & [34] \\ Spruce & \(24.7\pm 0.2\) & \(10.2\pm 0.1\) & \(35.0\pm 0.3\) & [35] \\ Sugarcane bagasse & \(46.1\pm 0.7\) & \(20.1\pm 0.9\) & \(20.3\pm 0.6\) & [36] \\ Sunflower stalk & \(34\pm 0.6\) & \(20.8\pm 0.8\) & \(29.7\pm 0.6\) & [37] \\ Water hyacinth & \(36.84\pm 0.8\) & \(27.7\pm 0.2\) & \(10.7\pm 0.4\) & [38] \\ Wheat straw & \(43.4\) & \(26.9\) & \(22.2\) & [39] \\ Willow sawdust & \(35.6\pm 0.9\) & \(21.5\pm 0.9\) & \(28.7\pm 0.2\) & [40] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Composition of different lignocellulosic substrates; cellulose, hemicellulose, and lignin content (%) on dry basis. Figure 2: Structure of lignocellulosic biomass and its biopolymers; cellulose, hemicellulose, and lignin. Cellulose is the major component of plant cell structure and is a homo-polymer made of \(\beta\)-1,4-glycosidic bonds, which give stiffness and stability, characteristic to l structure of the cell wall [41]. The principal unit of cellulose, D-pyran glucose, makes the crystalline and amorphous regions in the cellular arrangement. The orientation and direction that have the chains of cellulose is of vital importance and determine their function. In the primary wall are the first type of alpha helical, (lower molecular weight than the secondary wall) allowing the cell storing sugars and fluids [42]. On the other hand, secondary wall cellulose chains are rigid and straight to give the molecular structure to the cell [43]. Lignin is formed from the oxidation of phyldroxycinnamyl alcohols: p-coumaryl, coniferyl, and sinapyl. The formation of lignin involves three routes of biosynthesis: the shikimate pathway, the phenylpropanoid pathway and the synthesis of monolignols [46]. The units of lignin formation are: guaiacyl (G), syringyl (S), and p-hydroxyphenyl (H) [47]. The structure formed by three-dimensional and amorphous heteropolymers of lignin helps the cell in situations of stress, whether due to structural or metabolic damage, also serves as protection of the cell wall against pathogens [48].