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ABSTRACT: Biomass is an important renewable feedstock for the sustainable production of liquid transportation fuels and commodity chemicals. Lignin is a complex aromatic heteropolymer comprising roughly 15-25 wt% of biomass, and lignin’s recalcitrance has emphasized research into developing holistic, effective chemical and biological strategies for its valorization within next-generation biorefineries. Solvolysis of lignin from the plant cell wall is the critical first step in lignin depolymerization processes involving whole feedstocks, such as hardwood trees, although little is known about the complex transport phenomena governing lignin extraction at the particle scale. This seminar highlights insights into the internal and external microscopic geometries of poplar sawdust particles and their utility for constructing realistic, three-dimensional particle models with resolved microstructures. These well-defined particle models serve as a basis for computational fluid dynamics simulation of biomass pretreatment processes involving parallel chemical reactions and simultaneous heat and mass transfer. Methanol extractions of each lignin, hemicellulose, and cellulose are modeled to fit time-resolved experimental data generated among four representative poplar particle sizes. Intrinsic, transport-independent kinetic rate parameters are determined for the first time, capturing extraction and redeposition behaviors for each major cell wall component as decoupled from their diffusion behaviors. Crucially, lignin fragment diffusion is discovered to exhibit severe mass transfer resistances that dominate solvolysis kinetics in poplar particles exceeding as little as ~2 mm in length. These findings are critical to guiding modern biomass research and development, which largely emphasizes catalyst optimization in lieu of feedstock-specific limitations, offering a predictive platform for improving the design and scale-up of emerging biorefinery strategies.

 

SPEAKER BIO:  Dr. Nicholas (Nick) Thornburg will be presenting his postdoctoral research at the National Renewable Energy Laboratory (NREL) on understanding and decoupling mesoscale reaction-diffusion phenomena for the selective extraction of lignin from hardwood trees, as is relevant to emerging biomass pretreatment techniques for next-generation biorefineries.  Nick has a B.S. in 91���˶���Ƶ Engineering from Washington University in St. Louis and a Ph.D. in 91���˶���Ƶ Engineering from Northwestern University, in addition to industrial R&D experience with the Dow 91���˶���Ƶ Company and 3M. He is currently a 91���˶���Ƶ Reaction Engineer at NREL.