Improved Lignin Depolymerization for Higher-Value Products


Lignin is a heterogeneous aromatic biopolymer that accounts for nearly 30% of the organic carbon on Earth and is one of the few renewable sources of aromatic chemicals. As the most recalcitrant of the three components of lignocellulosic biomass (cellulose, hemicellulose, and lignin), lignin has been treated as a waste product in the pulp and bioenergy industries, where it is sometimes burned to provide energy. Creation of higher-value bioproducts from lignin will increase the economic viability of integrated biorefineries. Depolymerization is an important starting point for many lignin valorization strategies, because it can generate valuable aromatic chemicals and provide a source of low-molecular-mass feedstocks suitable for downstream processing. Commercial precedents show that certain types of lignin (lignosulphonates) may be converted into vanillin and other marketable products, but new technologies are needed to enhance the lignin value chain. Lignin’s complex, irregular structure complicates chemical conversion efforts, and known depolymerization methods typically afford ill-defined products in low yields (that is, less than 10-20 wt%). Researchers of the Department of Energy’s Great Lakes Bioenergy Research Center describe a method for the depolymerization of oxidized lignin under mild conditions in aqueous formic acid that results in more than 60 wt% yield of low molecular-mass aromatics. This facile C-O cleavage method was used to depolymerize aspen lignin, providing mechanistic insights into the reaction. Efficient lignin depolymerization and biomass refining have the potential to contribute to the commercial and economic viability of lignocellulosic biofuels.


Rahimi, A., A. Ulbrich, J. J. Coon, and S. S. Stahl. 2014. “Formic-Acid-Induced Depolymerization of Oxidized Lignin to Aromatics,” Nature 515, 249-52. DOI: 10.1038/nature13867.