Thermosetting polymeric materials have advantageous properties and are therefore used in numerous applications. In this study, it was hypothesized and ultimately shown that thermosets could be derived from comparably sustainable sub-components. A two-step procedure to produce a thermoset comprising of Kraft lignin (KL) and the cross-linker adipic acid (AdA) was developed. The cross-linking was activated by means of an acetylating agent comprising isopropenyl acetate (IPA) to form a cross-linking mixture (CLM). The cross-linking was confirmed by FTIR and solid-state NMR spectroscopy, and the esterification reactions were further studied using model compounds. When the KL lignin was mixed with the CLM, partial esterification occurred to yield a homogeneous viscous liquid that could easily be poured into a mold, as the first step in the procedure. Without any additions, the mold was heated and the material transformed into a thermoset by reaction of the two carboxylic acid-derivatives of AdA and KL in the second step.

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).

By extracting lignin, pulp production can be increased without heavy investments in a new recovery boiler, the typical bottleneck of a pulp mill. The extraction is performed by using 0.20 and 0.15 weight equivalents of CO2 and H2SO4 respectively. Herein, we describe lignin esterification with fatty acids using benign reagents to generate a lignin ester mixable with gas oils. The esterification is accomplished by activating the fatty acid and lignin with acetic anhydride which can be regenerated from the acetic acid recycled in this reaction. The resulting mass balance ratio is fatty acid/lignin/acetic acid (2 : 1 : 0.1). This lignin ester can be hydroprocessed to generate hydrocarbons in gasoline, aviation, and diesel range. A 300-hour continuous production of fuel was accomplished. By recirculating reagents from both the esterification step and applying a water gas shift reaction on off-gases from the hydroprocessing, a favorable overall mass balance is realized.

Organosolv pulping performed in a high-pressure Soxhlet extractor using carbon dioxide as a mild and recyclable acid is described. The system reached a liquid to wood ratio of 6.6 yielding 43 wt% of dissolving grade quality pulp from Populus trichocarpa. The set-up enabled to run reductive catalytic fractionation to yield a lipophilic lignin oil without affecting the performance nor the purity of the final pulp.

 Lignin is an abundant polymeric renewable material and thus a promising candidate for incorporation in various commercial thermoplastic polymers. One challenge is to increase the dispersibility of amphiphilic lignin in lipophilic thermoplastic polymers We altered Kraft lignin using widely available and renewable fatty acids, such as oleic acid, yielding more than 8 kg of lignin ester as a light brown powder. SEC showed a molecular weight of 5.8 kDa with a PDI = 3.80, while the T_g of the lignin ester was concluded to 70 °C. Furthermore, the lignin ester was incorporated (20%) into PLA, HDPE, and PP to establish the thermal and mechanical behavior of the blends. DSC and rheological measurements suggest that the lignin ester blends consist of a phase-separated system. The results demonstrate how esterification of lignin allows dispersion in all the evaluated thermoplastic polymers maintaining, to a large extent, the tensile properties of the original material. The impact strength of HDPE and PLA blends show substantial loss upon the addition of the lignin ester. Reconverting the acetic acid side stream into acetic anhydride and reusing the catalyst, the presented methodology can be scaled up to produce a lignin-based substitute to fossil materials.

Herein, a catalytic reductive fractionation of lignocellulose is presented using a heterogeneous cobalt catalyst and formic acid or formate as a hydrogen donor. The catalytic reductive fractionation of untreated birch wood yields monophenolic compounds in up to 34 wt % yield of total lignin, which corresponds to 76% of the theoretical maximum yield. Model compound studies revealed that the main role of the cobalt catalyst is to stabilize the reactive intermediates formed during the organosolv pulping by transfer hydrogenation and hydrogenolysis reactions. Additionally, the cobalt catalyst is responsible for depolymerization reactions of lignin fragments through transfer hydrogenolysis reactions, which target the beta-O-4' bond. The catalyst could be recycled three times with only negligible decrease in efficiency, showing the robustness of the system.

A series of phenolic bio-oil components were selectively hydrodearomatized by palladium on carbon into the corresponding ketones or alcohols in excellent yields using polymethylhydrosiloxane and water as reducing agent. The selectivity of the reaction was governed by the water concentration where selectivity to alcohol was favoured at higher water concentrations. As phenolic bio-oil examples cardanol and beech wood tar creosote were studied as substrate to the developed reaction conditions. Cardanol was hydrodearomatized into 3-pentadecylcyclohexanone in excellent yield. From beech wood tar creosote, a mixture of cyclohexanols was produced. No hydrodeoxygenation occurred, suggesting the applicability of the reported method for the production of ketone-alcohol oil from biomass.

This review discusses the challenges within the research area of modern biomass fractionation and valorization. The current pulping industry focuses on pulp production and the resulting cellulose fiber. Hemicellulose and lignin are handled as low value streams for process heat and the regeneration of process chemicals. The paper and pulp industry have therefore developed analytical techniques to evaluate the cellulose fiber, while the other fractions are given a low priority. In a strive to also use the hemicellulose and lignin fractions of lignocellulosic biomass, moving towards a biorefining concept, there are severe shortcomings with the current pulping techniques and also in the analysis of the biomass. Lately, new fractionation techniques have emerged which valorize a larger extent of the lignocellulosic biomass. This progress has disclosed the shortcomings in the analysis of mainly the hemicellulose and lignin structure and properties. To move the research field forward, analytical tools for both the raw material, targeting all the wood components, and the generated fractions, as well as standardized methods for evaluating and reporting yields are desired. At the end of this review, a discourse on how such standardizations can be implemented is given.