Lignin

Lignin Monomer

Lignin is a phenylpropane polymer that holds together cellulose and hemicellulose components of woody biomass. Lignin constitutes about 15 to 25 percent of the weight of woody biomass. Lignin has not yet been used as a raw material for industrial purposes in large quantities. Concerted attempts by pulp and paper research laboratories to develop new markets for by-product lignins have had only limited success (Bozell and Landucci, 1993). Production of low-molecular-weight compounds from kraft lignin, phenols in particular, has also not yet proved to be commercially competitive. This reflects the chemical complexity of lignin and its resistance to depolymerization. Nevertheless, a recent Department of Energy study concluded that pyrolysis of lignocellulosics could make production of phenolics and anthraquinone from lignin competitive, and the potential also exists to produce benzene, toluene, and xylenes from lignin via pyrolysis (Bozell and Landucci, 1993). Lignocellulose pretreatment will be a key step for realizing the presently untapped potential of abundant lignocellulosic materials found in wood (Malherbe and Cloete 2002). Until these higher value products emerge, lignin will continue to be burned to produce energy.