(534c) Pyrolytic and Electrochemical Upgrading of Lignins Extracted from Pretreated Biomass to Produce Liquid Fuel Intermediates and Value-Added Products

Pretreatment enhances the effectiveness of enzymatic strategies for depolymerizing the cellulose and hemicellulose fractions of plant biomass. Many different pretreatment strategies have been investigated, including the use of dilute acid, steam explosion, organosolv, alkaline hydrogen peroxide (AHP), and ammonia fiber expansion (AFEX). Extractive ammonia (EA) pretreatment, a more severe version of AFEX, recovers a separate lignin stream from biomass. Upgrading this lignin stream to create fuels and chemicals potentially adds value to decentralized processing depots or centralized biorefineries that practice EA pretreatment. One approach to valorizing this lignin stream is to deconstruct EA lignin using fast pyrolysis to create a lignin-derived bio-oil that is rich in phenolics. Fast pyrolysis involves rapid heating (400-600°C) in the absence of oxygen to create bio-oil, biochar and combustible gas. Upgrading of lignin bio-oil proceeds by electrocatalytic hydrogenation (ECH), preferably using electricity from wind and solar sources. In this study, model compounds that represent lignin bio-oil components were subjected to ECH under mild conditions using ruthenium on activated carbon as a catalytic cathode. To date, several such compounds have been successfully reduced to more stable forms, for example, phenol, guaiacol and syringol have been converted into cyclohexanol at appreciable yields and selectivities. In parallel to model compound studies, catalyst reusability studies have enhanced our understanding of electrocatalyst deactivation and methods for extending catalyst lifetime. By coupling fast pyrolysis and electrocatalysis for lignin deconstruction and upgrading, respectively, a major byproduct of alcohol fermentation can be valorized into fuels and chemical products. Integration of thermochemical, electrochemical and biochemical transformative pathways is paramount for realizing the full potential of plant biomass for displacing petroleum.