Lignin-first fractionation of lignocellulosic biomass from agricultural residues

Brienza, Filippo [UCL] Debecker, Damien P. [UCL] Cybulska, Iwona [UCL]

Lignin monomers and short-chain oligomers, as well as purified cellulose and hemicellulose fractions, represent extremely valuable chemicals for green chemistry applications, including biofuel production, polymers manufacturing and pharmaceutical applications. Currently, no method is available that would offer a means to achieve an efficient, industrially feasible, process for the fractionation of lignocellulose into such interesting intermediates. This research is targeting the controlled lignin extraction and depolymerization from agricultural residues (e.g. wheat straw, corn stover) through catalytic hydrogenolysis and hydrogenation during the "solvolysis" process, which yields lignin oligomers and phenolic monomers(guaiacyl, syringyl and coumaryl alcohol derivatives). The influence of operating conditions on delignification, lignin depolymerization and carbohydrate retention has been investigated. Catalysts based on transition metals (e.g. Ni) have been studied with the goal of replacing the more expensive precious metal catalysts employed in the current research. In parallel, the possibility of eliminating the hydrogen gas used in the process, by substituting it with hydrogen donor solvents, has been inspected. The intermediates produced within the process (including the lignin oil and the carbohydrate fraction) have been characterized to assess its performance, as well as to evaluate the most favorable routes for further transformation and valorization of the obtained products. Process optimization has been performed aimed at reducing the process severity, while maximizing the yield of lignin mono/oligomers and recovered carbohydrates, thus targeting future industrial implementation.