Lignin (an aromatic macromolecule in biomass), the only renewable source of aromatics, is currently treated as waste and under-utilized. A more appealing and value-added use of lignin is as a precursor for the production of aromatic chemicals. The depolymerization of lignin selectively into its monomers can be achieved by the appropriate combinations of solvent, catalyst, and reaction conditions. However, due to the considerable complexity and natural variation in the molecular structure of lignin, mechanistic studies of catalytic lignin depolymerization are challenging. Beyond that, lignin depolymerization usually (1) requires relatively high temperature (above 200 °C) and pressure (above 80 bar); (2) involves co-existence of solid, liquid and gas phases; and (3) differs from typical catalytic reactions due to the macromolecular nature of the substrate. In this study, we have synthesized 13C labeled lignin model polymers with only β-O-4 linkages and hydroxyphenyl monomers of different molecular weights to perform in-situ magic angle spinning (MAS) solid-state nuclear magnetic resonance (NMR). This project leverages the unique high-temperature and –pressure MAS NMR technology at the Pacific Northwest National Laboratory (PNNL). Using the 13C labeled lignin model polymers at different reaction conditions, we were able to monitor the real-time mechanistic reaction network of lignin depolymerization while also accounting for the potential effects of the macromolecular size of lignin.
In 2012, Marcus Foston became a professor in the Department of Energy, Environmental & Chemical Engineering at Washington University in St. Louis and was promoted to Associate Professor in 2019. He received his PhD in Polymer Chemistry in the Material Science and Engineering Department at the Georgia Institute of Technology in 2008. His postdoctoral fellowship was conducted as part of the DOE BioEnergy Science Center and under the guidance of Dr. Arthur Ragauskas, a Fulbright Distinguished Chair in Alternative Energy, in the School of Chemistry and Biochemistry at Georgia Institute of Technology. During this period, his research focused on the study of the chemistry, dynamics, and mechanism of deconstruction of lignocellulose to form biofuels, biomaterials, and biocomposites. Professor Foston’s research program seeks to develop innovative and novel routes to exploit and utilize lignocellulosic biomass and waste plastics. His primary research themes are: (1) Conversion of lignocellulosic biomass or waste plastics into chemicals using liquid-phase, heterogeneous catalysis. (2) Interfacing the catalytic depolymerization with microbial upgrading process. (3) The synthesis novel biomass-derived materials.
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