Lignin Component aromatics

When considering biomass as a source of chemical feedstock, it is also important to remember that it is not a homogeneous organic structure. The carbohydrate structures of terrestrial plants are composed of both five-carbon and six-carbon sugar polymers. The lignin component, which binds the polymers together, is an aromatic polymer of nominally propyl-methoxyphenols. In addition, there are proteins and fatty acids/oils, as well as the trace biocomponents that incorporate much of the mineral content. Therefore, processing biomass to chemical products must take into consideration both its bulk chemical structure and its components. 

The absorption of UV light by wood occurs mainly due to the absorption by lignin (an aromatic polymer wood component) that is a good absorber of UV radiation comparatively with cellulose (the main polysaccharide from wood stmcture). It seems that lignin acts as a photo-sensitizer in the degradation of the... 

Lignin. Although aromatic amino acids are ubiquitous and are essential as food components, in sheer amount, lignin takes first place among the aromatic plant products. 

It is possible to indentify the ratios of carbohydrates (110-50 ppm), the ratio of aromatics (lignin) (150-130 ppm) and aliphatic acids and sterols (175 ppm, 40-15 ppm) from the spectra. In sample I cellulose signals were dominant, in sample II, on the other hand the aliphatic fractions were the major component. Sample III represented a balanced mixture of all three material groups. It was also possible to indentify the phosphate signal at 0 ppm by means of P-31 spectroscopy. 

The inability to solubilize aromatic components of suberin-enriched preparations by the methods used for lignin suggests that suberin structure is distinctly different from that of lignin, probably due to the aliphatic cross-linking and the higher degree of condensation present in suberin. 

Lignin comprises about 17-33% of the dry weight of wood. It is a complex aromatic polymer which appears to function both as a strengthening agent in the composite wood structure and also as a component which assists in the resistance of the wood towards attack by micro-organisms and decay. 

As to the origins of the major N compounds identified, it is possible that at least a portion of some of these compounds are pyrolysis products of amino acids, peptides, proteins, [18] and porphyrins (a component of chlorophyll), [19] or originate from the microbial decomposition of plant lignins and other phenolics in the presence of ammonia. [20] Of considerable interest are the identifications aromatic and aliphatic nitriles. Nitriles can be formed from amines with the loss of 2 H2, from amides with the loss of H20, and also by reacting n-alkanoic acid with NH3. [21] The detection of long-chain alkyl- and dialkyl-nitriles points to the presence in the soil or SOM of long-chain amines... 

Aromatic compounds are present but do not constitute a predominant part of the molecule the polyphenollc and polyaromatic components are low in concentration and exhibit low degrees of substitution Aliphatic side chains are attached to the aromatic core, but due to the participation of lignin degradation products, aromatic moieties are more abundant... 

Elforts have been made to characterize the nature and content of individual components that are present in the low-molecular-mass fraction of the total mill effluents, which include the spent chlorination and alkali extraction stage liquors [2,4]. Approximately 456 types of compounds have been detected in the conventional bleach effluents, of which 330 are chlorinated organic compounds [22]. The compounds may be lumped into three main groups, namely, acidic, phenolic, and neutral (Table 2). Acidic compounds are further divided into the five categories of acids fatty, resin, hydroxy, dibasic, and aromatic acids. The most important fatty acids are formic and acetic acids. The dominant resin acids are abietic and dehydroabietic acids. Among the hydroxy acids identified, glyceric acid predominates. Dibasic acids such as oxalic, malonic, succinic, and mafic acids are derived from the lignin and carbohydrate fraction... 

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