(541a) In-Situ Neutron Scattering of the Lignin Liquid-Phase Depolymerization with a Heterogeneous Catalyst

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 applied Small Angle Neutron Scattering (SANS) on lignin samples to probe their polymer coil size and conformational changes that occur at reaction conditions and upon interaction with copper-doped porous metal oxide catalyst. This project leverages the unique high-temperature and –pressure neutron cell technology at the Oak Ridge National Laboratory (ORNL). In-situ SANS studies will provide a means to probe changes in the structure of lignin as a function reaction conditions (i.e., time, temperature, and the presence of catalyst) while eliminating any potential structural artifacts that would be caused by the reactor quenching and/or sample preparation occurring in ex-situ experiments.