TURNING LIGNIN INTO VALUE: SUSTAINABLE RECOVERY AND CATALYTIC OXIDATIVE CONVERSION

The transition from fossil-based resources to renewable biomass is a critical challenge for modern society. Lignocellulosic biomass, primarily composed of cellulose, hemicellulose, and lignin, offers a sustainable platform for producing high-value chemicals. However, the structural complexity and recalcitrance of lignin—a heterogeneous macromolecule formed from phenylpropanoid units—limit its efficient utilization. This Thesis explores innovative strategies to improve lignin isolation and depolymerization, focusing on Green Chemistry principles. The research is divided into two primary areas: the development of a photo-redox catalytic system for oxidative cleavage of vicinal diols and the optimization of lignin extraction using Deep Eutectic Solvents (DESs). Initially, the study investigates the photocatalytic activity of a vanadium(V) aminotriphenolate complex (VOTPA(Cl,Cl)). This system demonstrates high efficiency in the aerobic oxidative cleavage of C–C bonds in vicinal diols, which serve as models for lignin linkages. Utilizing blue light and molecular oxygen at room temperature, the catalyst achieved quantitative yields of carbonyl compounds in green solvents like anisole. To enhance the scalability and safety of this process, the reaction was successfully transitioned from batch to continuous flow conditions. The flow setup maximized light absorption and mass transfer, resulting in significantly accelerated reaction rates and improved energy efficiency. The second half of the Thesis addresses the "lignin-first" challenge of isolating high-quality, "native-like" lignin from biomass. Traditional extraction methods often destroy the labile β-O-4 ether bonds essential for downstream valorization. This work introduces a novel cyclic extraction approach and a subsequent flow-through system utilizing a choline chloride/lactic acid DES. By rapidly removing extracted lignin from the heated reaction environment, these methods prevented secondary degradation. Results from 1H-13C HSQC-NMR, 31P-NMR and GPC analysis confirmed that these innovative setups achieved near-quantitative isolation yields (up to 98% at 120°C) while maintaining an exceptional retention of native β-O-4 linkages—achieving values nearly identical to native biomass. This research provides a robust framework for integrating advanced catalysis and intensified processing into sustainable biorefinery schemes.