Catalytic valorization of lignocellulose : Direct and sidestream upgrading approaches

This work aims to explore different approaches for the valorization of lignocellulosic biomass. In this regard, two different strategies are presented: the catalytic upgrading of lignocellulose derivatives from industrial streams, such as pyrolytic oil and kraft lignin, and the direct catalytic fractionation of woody biomass. The first approach is explored in Paper I and II, while the second in Paper III and IV. Different phenolic compounds were hydro-dearomatized using a heterogeneous catalytic system based on Pd/C and polymethylhydrosiloxane/H2O as a liquid hydrogen source. High yields of either cyclohexanones or cyclohexanols were achieved in high selectivity by varying the concentration of water. To prove the broad applicability of the method, commercially available bio-oils such as beechwood tar creosote and cardanol oil underwent hydrodearomatization using the developed catalytic systems (Paper I). Kraft lignin, a byproduct of the paper manufacturing industry, has been valorized by steering its solubility properties through the production of a lipophilic lignin oil suitable for hydrotreatment. The enhanced solubility allowed its blending in common refinery carriers and full hydrodeoxygenation yielding hydrocarbons in the gasoline-diesel range. A particular focus was set on the mechanistic study of the esterification where a 13C labeling analysis was performed (Paper II). Untreated birch wood was fractionated into its components while lignin was consequently depolymerized into monophenolic compounds. Cobalt was scrutinized to replace noble metals in reductive catalytic fractionation by synthetizing a heterogeneous catalyst supported on nitrogen-doped carbon. We found that adjusting the pH of the reaction medium affected the yields of the reaction. Under optimized conditions, monophenolic compounds could be obtained in up to 34 wt% yield relative to initial lignin. The role of the catalyst and reductants was investigated (Paper III). The last chapter describes a pulping system able to parallelly perform the glucan purification and the catalytic upgrade of the lignin by-products while avoiding the contamination of the pulp with the heterogeneous catalyst. The system is based on a high-pressure Soxhlet combined with the ethanol-water organosolv, where Pd/C was selected as the heterogeneous catalyst. Using only CO2 as the acid source, lyocell grade dissolving pulp was produced in addition to lignin oil (Paper IV)