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Hydrothermal Liquefaction A Promising Technology for High Moisture Biomass Conversion
Published in Jaya Shankar Tumuluru, Biomass Preprocessing and Pretreatments for Production of Biofuels, 2018
Ankita Juneja, Deepak Kumar, Jaya Shankar Tumuluru
Lignin is the most complex compound in lignocellulosic feedstocks and is highly resistant to degradation. Chemical structure of lignin is cross-linked phenolic heteropolymers with p-hydroxyphenyl-propanoid units held together by C–C or C–O–C bonds. Trans-p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol are the three monomeric building blocks of lignin (Bobleter, 1994). Lignin decomposes over a broad range of temperature as the scission of various oxygen functional groups occurs at different temperatures due to their thermal stabilities (Brebu and Vasile, 2010). Lignin degradation is shown to follow Arrhenius equation with variation in activation energy based on the method of isolating lignin (Schniewind, 1989). For instance, the activation energy for the lignin processed in sulfuric acid was 46 kJ/mol (Beall, 2007), whereas it was calculated to be 37 kJ/mol for Kraft-Pine lignin (Zhang et al., 2008). The similar activation energy (39.35 kJ/mol) was determined for guaiacol (model compound of lignin) decomposition in near-critical and supercritical water (Kanetake et al., 2007).
Research on the electrochemical degradation and hydrogen generation of Fraxinus mandshurica by polyoxometalate
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Jiayue Ma, Fengrong Gong, Xiuyuan Ma, Lihui Jiang, Ting Wang
As shown in Figure 1, solid wood is mainly composed of lignin, cellulose, and hemicellulose (Rutherford et al. 2012). Lignin is rich in aromatic ring structural units, which are composed of three precursors, namely sinapyl alcohol, coniferyl alcohol, and p-coumaryl alcohol (Tagami et al. 2019). This makes lignin available as a source of aromatic small molecule chemicals and for use in energy, materials, and other applications (Duval et al. 2016). Hemicellulose is a generic term for a group of complex glycans containing xylose, xylan, glucomannan, mannans, and β-(1,3 and 1,4)-glycans (Pauly et al. 2013), which is easily degraded due to its amorphous structure caused by the presence of branched chains and acetyl groups. Cellulose, the most abundant part of the wood, is a large molecule made up of glucose units in a regular and ordered arrangement. Cellulose has many inter- and intra-molecular hydrogen bonds which make it more stable (Jarvis 2003). These abundant chemical units in the solid wood are the theory basis for the conversion of wood waste to valuable chemicals.
Characterization of kraft pulp delignification using sodium dithionite as bleaching agent
Published in Chemical Engineering Communications, 2020
Jishnu Krishnan, Susmith Sunil Kumar, R. Krishna Prasad
Lignin is a group of cross-linked phenolic polymers (p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol) which are essential components of cell wall. Lignin constitutes approximately 20–35% by weight in most of the woods. The primary and secondary wall which contains the wood fiber are held together by lignin. Lignin promotes reactions that involve electron transfer, radicals and oxidation. Lignin imparts rigidity and strength to wood and the degree of polymerization of lignin ranges from 19.5 to 30.6 (Kratzl et al., 1973; Singh and Dillner, 1979).
Chemical characterization of acid-pretreated renewable resources: effect of pretreatment time
Published in Biofuels, 2022
Mustafa Germec, Ali Ozcan, Irfan Turhan
Renewable resources such as agricultural wastes, forestry residues, agro-industrial wastes, wood wastes, grasses, waste papers, wastes of the food industry, municipal wastes, animal manures, and bioenergy crops are the most abundantly available natural sources in the world (approximately 10–50 billion tons annually worldwide). They consist of cellulose (40–50%), hemicellulose (25–30%), lignin (15–20%, an aromatic polymer), and other extractives such as fatty acid components, wax, terpenoids, resins, and tannins [1–5]. Therefore, renewable resources are rich in terms of carbohydrates such as pentoses and hexoses, and thus they can be converted to value-added products, in particular second-generation biofuels, by fermentation [5–7]. Cellulose in the form of lignocellulose, which is a homo-polysaccharide found in the cell wall, is the most abundant organic compound in the world (about 1.5 × 1012 tons per year). It has an unbranched structure and consists of D-glucose subunits joined with β-1,4 glycosidic bonds. Hemicellulose is the second most abundantly available biopolymer in the world after cellulose; it is a branched heteropolysaccharide since it contains D-glucose, D-mannose, D-galactose, L-arabinose, D-xylose, and uronic acids (D-GA, D-4-O-methylgalacturonic, and D-galacturonic acids). Furthermore, hemicellulose is bonded to cellulose with hydrogen bonds and to lignin with covalent bonds. One of the major components in the lignocellulosic structure and the major organic compounds in nature is lignin, which is a mainspring in the development and growth of plants and plays an important role in the carbon cycle in nature. Lignin is a complex aromatic and hydrophobic hetero-polymer and consists of three major phenolic components, coniferyl alcohol, sinapyl alcohol, and p-coumaryl alcohol. It also increases the rigidity, resistance, and integrity in the cell wall of renewable resources [1, 2, 5, 7–9].