Lignin and lignocellulose

Table 6.4.2. Structure and mass spectral characteristics of thioacidolysis products from various isolated lignins and lignocelluloses...

The procedure described below, a modified version of the method developed by Adler et al. (1958) and Gierer et al. (1964), is applicable to both lignin and lignocellulosic samples. The general procedure consists of oxidation of the sample with an aqueous sodium periodate solution and a direct measurement of the liberated methanol in the presence of an internal standard. 

Crestini C, Crucianelli M, Orlandi M, Saladino R (2010) Oxidative strategies in lignin chemistry a new environmental friendly approach for the functionalisation of lignin and lignocellulosic fibers. Catal Today 156 8... 

Alternatively, lignocellulose can also be hydrolyzed to liberate the lignin and de-polymerize the polysaccharides to sugars. The sugars can subsequently be converted into various fuel and chemical components via chemical or biological routes. 

Various solvents are being investigated to dissolve lignocellulosic materials. Some approaches focus on the selective depolymerization and extraction of lignin and hemicellulose as pre-treatment to produce clean cellulose fibers for subsequent fermentation or for pulping. Other approaches attempt to dissolve the whole lignocellulose with or without depolymerization. The liquefaction processes that are carried out at high temperature (>300 °C), and produce a complex oil mixture, are discussed above with the pyrolysis processes. 

Lignocellulose biomass is a mixture of phenolic lignin and carbohydrates -cellulose and hemi-cellulose. It grows abundantly on earth and is largely available as agricultural and forestry residues. Lignocellulose can be converted via four major routes pyrolysis, gasification, hydrolysis and fermentation. 

Pretreatment of Substrate. Several different lignocelluloses were pretreated with NaOH. This pretreatment partially solubilizes the hemicelluloses and lignin and swells the cellulose so that the organism can utilize it for its growth and for production of a cellulase system in SSF. The treated lignocelluloses were not washed. The NaOH treatment is done with a minimum amount of water so that, after the addition of nutrient solution and inoculum, the moisture content is less than 80% wt/wt and there is no free water in the medium. More water was added to make suspensions of different lignocellulosic substrates of the desired concentration (1% or 5%) for liquid-state (submerged) fermentation (LSF). 

As far as the ethylene glycol lignin is concerned, it has been shown to be a native-like lignin which can be produced and recovered by direct solvolytic treatment of the initial lignocellulosic substrate. It would also be possible to remove the hemicelluloses via an aqueous/steam treatment prior to solvolytic separation of the lignin and cellulose. Such an option would facilitate the recovery of the three main constitutive fractions of lignocellulosics in significant yields. Work in this direction is now underway. 

Of the many physical and chemical procedures thus far applied to enhance lignocellulose reactivity (1), fine grinding appears to offer the most direct response to both lignin and crystallinity. When the grinding is done in a vibratory ball mill, particle size can be reduced to micron dimensions, with attendant expansion of external surface area, and crystallinity can be essentially eliminated (2). This combination of events markedly influences carbohydrate accessibility and, hence, the degree of response of a milled lignocellulosic material to chemical, enzymatic, and microbiological attack. 

Carbohydrates would be the predominant raw materials for future biorefineries. The major polysaccharides found in nature are cellulose, hemicellulose and starch (see Chapter 1). These molecules would be mainly utilised after they are broken down to their respective monomers via enzymatic hydrolysis, thermochemical degradation or a combination of these two. Cellulose and hemicellulose, together with lignin, constitute the main structural components of biomass. Starch is the major constituent of cereal crops. This section would focus on the potential utilisation of carbohydrates and lignocellulosic biomass for chemical production. 

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