Lignin feedstocks

Various processes have been developed for hydrolyzing lignocellulose to its major constituents, i.e., to sugars and (partly) depolymerized lignin. The lignin is usually precipitated from the aqueous solution and either used as chemical feedstock or burned as process fuel. The aqueous sugar solution is then applied for fermentation to ethanol after neutralization and purification. 

Agricultural residues (stem, leaves, etc.) currently left in the fields after harvesting are made of cellulose, hemicellulose, and lignin. They are not competing with the feedstock for the food industry. 

The chemical and enzymatic oxidative degradation of lignin (and coal) is used to obtain not only vanillin and benzoic acid, but also other aromatics (Baciocchi et al. 1999, references therein). In principle, lignin could be a major nonfossil and renewable source of aromatic compounds, a feedstock for synthesis of useful products. The problem deserves finding new ion-radical routes to cleave lignin. At present, there is some shortage in oil, gas, and even coal, which had usually been well-available natural sources of aromatics. In the near future, biomass may (and must) replace fossil-originated materials in the manufacture of commercial carbon-based products. 

Municipal Sewage Treatment Plant. The reactors were batch-fed daily an RDF (refuse derived fuel) processed MSW feedstock obtained from Future Fuels Inc. in Thief River Falls, MN. The processed MSW feed contained 52% of dry weight (DW) cellulose, 20% lignin-plastics, 2% ash, and 26% acid-detergent solubles (% DW as determined by the acid-detergent-fiber assay (63)). The MSW feedstock was added to a nutrient solution at 5% w/v for daily feeding as previously described (55). 

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