Removal of Lignin

The ubiquity of lignin in plant tissue presents an obstacle to the removal and purification of xylan. Lignin retards or prevents the complete solution of xylan either because of mechanical obstruction or perhaps by reason of attachment through as yet unidentified covalent bonds. Furthermore, lignin is partially soluble in the various aqueous alkaline solutions used for dissolving xylan and, consequently, poses a purification problem in various subsequent steps designed to isolate the pure polysaccharide. 

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Wang, M.H.S., Granstrom, M.L., Wilson, T.E., and Wang, L.K., Removal of lignin from water by precipitate flotation, Journal of Environmental Engineering Division, Proceedings of the ASCE, 100 (EE3), 629-640, 1974. 

Cellulose is the primary structural component of the cell wall and, after removal of lignin and various other extractives, it is also the primary structural component of paper. Chemically, it is a semicrystalline microfibrillar linear polysaccharide of /M,4-linked d-glucopyranose (Figure 2.6). 

In its simplest form, mechanical pulping involves the conversion of raw wood into paper-making pulp by use of mechanical means only and does not involve the removal of lignin. There are many... 

Oxidants are occasionally added to the hydrolysis mixture to favor the removal of lignin. For instance, the co-feed of 02 or air appeared beneficial to the deligni-fication efficiency of a lime-catalyzed hydrolysis step [57]. Similar improvements are also reported for the co-feed of H202 to formic or acetic acid hydrolysis [58],... 

In addition to the normally suggested, sample pre-treatment procedures used prior to l.c. injection to avoid column contamination, Cig bonded silica-gel cartridges are particularly useful for removal of lignin-derived degradation-products that occur in biomass-conversion samples. 

In lignin, there are attendant ketone (sometimes, qninone) chromophoric moieties that give it a yellow/brown color. Cellulose is a white substance, which provides the desired strength and brightness properties to the paper products. The strength and whiteness of a paper product depends on the extent of removal of lignin from the pnlp fibers. Row woods contain as mnch as 20-30% lignin. 

Modern paper is made from wood pulp, largely cellulose, which is obtained by the removal of lignin from debarked wood chips by use of chemical treatments with sodium hydroxide, sodium sulfite, or sodium sulfate. Newsprint and paperboard, which is thicker than paper, often contains a greater amount of residual lignin. 

Cellulose is sometimes used in its original or native form as fibers for textile and paper, but is often modified through dissolving and reprecipitation or through chemical reaction. The xanthate viscose process, which is used for the production of rayon and cellophane, is the most widely used regeneration process. The cellulose obtained by the removal of lignin from wood pulp is converted to alkali cellulose. The addition of carbon disulfide to the latter produces cellulose xanthate. 

Holocellulose Cellulosic material obtainable from wood after removal of lignin. The term therefore means total carbohydrates (cellulose and hemicellulose) present in the wood (Refs 1 2) Ritter (Ref 3) succeded in isolating holocellulose from wood pulp by repeated chlori-nations, followed by extraction with alcohol containing 3% of monoethanolamine. The resulting product was white but changed color on standing... 

Chlorous acid is of particular interest because of its use for the removal of lignin and other noncarbohydrate components from woody tissue without... 

Effect of Oxygen Delignification on Removal of Lignin and Yield of Carbohydrates... 

Hemicellulose Group of carbohydrates found in the cell wall in more or less intimate contact with cellulose. The hemicelluloses are more soluble than cellulose and much more readily hydrolyzed into sugars. Holocellulose Total carbohydrate fraction of wood remaining after the removal of lignin and solvent extractable substances. 

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