In this thesis work, formic acid (FA) proved to be an effective in-situ hydrogen donor for the reductive depolymerization of kraft lignin (KL). At the optimum conditions without catalysts, i.e., 300

Hydrolysis lignin (HL) was liquefied employing 50/50 (v/v) water–ethanol mixture for the preparation of bio-based polyols/rigid polyurethane foams.

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Kraft and organosolv lignin (KL and OL) were depolymerised efficiently in supercritical acetone in the presence of various hydrogenation catalysts (supported metal, e.g., Ni, Ru, Mo, W) and 100 bar hydrogen in the temperature range of 250–350 °C. Under the optimal conditions with Ru/C or FHUDS‐2 catalysts at 350 °C for 1 h, the yield of depolymerised Kraft lignin (DKL) or depolymerised organosolv lignin (DOL) was over 95 wt %. The weight average molecular weight of the lignin was reduced significantly from 10 200 (for KL) to 1020 g mol−1 (DKL) and from 2600 (OL) to 900 g mol−1 (DOL). The oxygen and sulfur contents of Kraft lignin were reduced by 24 and 96 %, respectively. The reductive depolymerisation treatment also decreased the amount of aliphatic hydroxyl groups and increased the amount of aromatic hydroxyl groups in the depolymerised lignin products.

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The fast-growing demand for renewable fuels and chemicals, together with environmental concern, has inspired the study of lignin. However, the valorization of lignin is challenged by its large molecular structure and oxygen content. Catalytic hydroprocessing of lignin is the effective depolymerization for producing fuels and chemicals. The aims of this work were the implementation and study of the role of a novel and inexpensive bimetallic catalyst, MoRu/AC, in the reductive depolymerization (hydroprocessing) of hydrolysis lignin. The increase in the reaction temperature, between 200 and 340 °C, dramatically enhanced the hydrogen content of the bio-oils relative to the feed. The MoRu/AC catalyst exhibited excellent activity in the hydrogenation and produced bio-oils with a substantially increased H/C ratio, suggesting enhanced hydrodeoxygenation activity of the MoRu/AC. The catalyst at optimum temperature, 340 °C, significantly promoted the hydrogenation, and the H content in the bio-oil was 1.5 times of that in the feed. The results demonstrated that the phenolic compounds were the main component in all the produced biooils. This confirms that hydrolysis lignin can be easily depolymerized at the temperature range of 200−340 °C in the presence of the MoRu/AC catalyst.

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