Ethanol Organosolv Lignin Depolymerization with Hydrogen over a Pd/C Catalyst

The effect of a 3% Pd/C catalyst on the depolymerization of the ethanol organosolv lignin (EOL) was studied in ethanol at 300–400 °C and 10–50 bar H₂ pressure. The EOL depolymerized to monoaromatic compounds, oligomers and larger lignin fragments in both catalytic and non-catalytic experiments. In addition, char was formed simultaneously due to repolymerization. The commercial Pd/C catalyst influenced the content of the bio-oil and gas fraction through the secondary reactions of the smaller product molecules. However, the EOL decomposition occurred mainly thermally and possibly autocatalytically due to the inert nature of the catalyst support. The effect of the catalyst on the monoaromatic product distribution was remarkable. With the catalyst, most of the identified products contained a saturated side chain produced by hydrogenation, whereas without the catalyst, the product distribution was wider, with a large portion of products exhibiting unsaturated and carbonyl side chains. Additionally, the monoaromatic compounds formed in the presence of the catalyst had longer side chains than the components formed in non-catalytic experiments.