EECE SEMINAR - Nicholas Thornburg

Dec 6, 2019
11:00 AM
12:00 PM
Brauer Hall, room 12

Nicholas Thornburg
NREL

Much ado about (almost) nothing: understanding mesoscale reaction-diffusion phenomena governing lignin extraction from hardwood biomass for next-generation biorefining

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 upfront valorization within next-generation biorefineries. Solvolysis of lignin from the plant cell wall is the critical first step in lignin-first depolymerization processes involving whole feedstocks, such as hardwood trees, although little is known about the strongly coupled reaction kinetics and transport phenomena that govern effective rates of lignin extraction. This seminar presents an experimentally validated simulation framework that incorporates feedstock characteristics such as external particle morphologies, internal microstructure, heat and mass transfer, and parallel chemical reactions for methanol-based extraction of poplar as the example fractionation process. Methanolytic extractions of lignin, hemicellulose, and cellulose are modeled to fit time-resolved experimental data generated using four particle size distributions within the heterogeneous bulk feedstock. Intrinsic, transport-independent kinetic rate parameters are determined for reversible kinetic rate laws of pseudo-first order in each species, capturing extraction and redeposition behaviors for each major cell wall component decoupled from their diffusion behaviors. Crucially, lignin fragment diffusion is predicted to compete on the same time and length scales as reactions of lignin for standard sawdust particle sizes, with severe mass transfer resistances predicted to dominate solvolysis of poplar particles exceeding as little as ~2 mm in length. These findings are key to guide lignin-first process research and development, which largely emphasizes catalyst optimization in lieu of feedstock-specific limitations in terms of feedstock-specific limitations, offering a predictive platform for improving the design and scale-up of emerging biorefinery strategies.