Collaborative Research: Towards a Generalized Microkinetic Description of Lignin Liquefaction

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Lignin is an abundant natural resource whose higher carbon content, when compared to cellulose and hemicellulose, makes it a very attractive renewable feedstock for producing fuels and chemicals. Lignin liquefaction is a promising process for converting this underutilized resource into monomeric phenols that can be easily upgraded to fuels and chemicals, but the underlying chemical kinetic processes are not well understood. This collaborative research project aims to develop a rational framework that integrates modelling and experimental tools to explicitly account for lignin and its oligomeric intermediate chemical structures at relevant liquefaction conditions in the presence or absence of solvents.Lignin liquefaction can be conducted in aqueous environments (hydrothermal liquefaction), in organic solvents (solvolysis), in ionic liquids or in solvent free conditions (pyrolysis). Assigning a realistic chemical formula to lignin and its oligomeric intermediates is one of the major challenges to rationally describe and control lignin liquefaction reactions. The mechanisms by which solvents and additives impact liquefaction reactions are also poorly understood. Because of this, lignin liquefaction remains an art rather than a science. The main goal of this project is to develop a rational micro-kinetic framework based on detailed micro-kinetic models describing depolymerization and repolymerization reactions and intermediate products removal mechanisms during lignin liquefaction. The practical goal is to use this mathematical model and experimental tools to identify suitable lignin liquefaction strategies in the presence of solvents and acid-base catalysts to maximize mono-phenol production which will facilitate further bio-oil upgrading in existing infrastructure. In addition to training two graduate students the principal investigators plan to host female and underrepresented minority high school students in their laboratories as summer research interns through the Summer Research Opportunity Program at Northwestern University and the Pacific Northwest Louis Stokes Alliance for Minority Participation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.